text:
Is there any evidence that the Litecoin network is significantly affected by botnet mining?
Litecoin uses a hashing algorithm that, so far, is best run on CPUs rather than GPUs.
Because most computers are not purchased for gaming and don't have powerful GPUs (which would have been useful for Bitcoin mining, at least until ASICs arrived on the scene), it would probably be far more profitable for a botnet to mine litecoins than bitcoins.
At the current Litecoin/Bitcoin exchange rate, the total litecoin network generates 216BTC worth of litecoins per day in block rewards (the Bitcoin network provides 3600BTC/day), which provides a substantial profit incentive to someone running a botnet.
Is there any evidence that botnets are responsible for a substantial amount of litecoin mining? Could this be detected?
Is there any known malware that mines Litecoin?

Related: http://bitcoin.stackexchange.com/q/1439/516

I have the privilege of answering your question a year later, where GPUs have taken over Litecoin and all of its derivatives. Currently, botnets would be better off mining a CPU coin like Primecoin.
That said, there is evidence of botnet mining for both Litecoin and Primecoin.


text:
What is a good resource to help newbies choose their first wallet/s?
While editing the Bitcoin Newb Guide, I realized I can't find a single page that covers all major clients in a Newb-friendly manner.

bitcoin.org doesn't seem to mention web wallets such as My Wallet
The wiki page is not IMO newb-friendly ... one big table, no clear way for a newb to decide which wallets he should try out. Yes, the features are listed in the table, but a newb won't understand them.

What is the best objective resource to help newbs choose their first wallet/s?
Requirements:

Objective source (as much as possible)
Updated Frequently, preferably user editable / reflects user votes
Includes major desktop clients
Includes major web wallets / mobile wallets
Noob Friendly - just dumping all clients in a big table will scare off noobs. I want a page that, while giving out sufficient information, is well structured and will not scare noobs. The Wiki Page is a good counter example.

"Just use blockchan's mywallet" is the best guide IMHO

I'm new to bitcoin, but I just opened an account with coinbase.com to get started.

@Lohoris: no, blockchain.info's web wallet works OK, but their wallet apps (both Android and iOS) are a disaster. Highly NOT recommended for beginners, it will only frustrate them.

And and do note the distinction between "the blockchain" (an important part of the Bitcoin technology) and "blockchain.info" which is an independant 3rd party website offering some Bitcoin-related utilities and services. Big difference.

@MaǳiKoǌo I've had a few beginner friends using them successfully, no problem. No clue why you claim they are a disaster. They can be improved a lot, surely, but disaster is another planet.

Essentially it boils down to the tradeoffs between security and convenience.
Instawallet is incredibly convenient, but not all that secure (as no password is required, and if you lose the URL, you lose the ability to spend the funds.)
Paytunia was a great shared (hosted) EWallet for a beginner, and there is a mobile app (for Android). A new version of Paytunia is in the works for a 2014 release.
Blockchain.info/wallet is a great hybrid (browser-based) wallet and also has a mobile app (for Android, and for Cydia / jailbroken iPhones). Configured properly, with backups sent to your e-mail inbox, this is probably the best combination of security and convenience.
If you only need a mobile wallet, the BitcoinSpinner works well also.

http://en.bitcoin.it/wiki/EWallet
http://en.bitcoin.it/wiki/Mobile_Payment_Apps

I've just downvoted this answer, because it is outdated with some examples not even operating anymore. I suggest that you check out the other answers as well.

I'd recommend to read up on Bitcoin to understand what you're doing. Then you can find an overview of wallets on bitcoin.org, but for a quick start, the fastest way to get started is:

Desktop (Windows/Mac/Linux) : Electrum or MultiBit
Android : Bitcoin Wallet by Andreas Schildbach
iOS : Bread Wallet
Windows phone : Get an Android phone instead

These are all fairly easy to use, and don't bother you with all kinds of advanced options.

This post was adapted from my answer on How to get started with a Bitcoin wallet.

Multibit has been deprecated for four years now. The Android Play store has numerous wallets named "Bitcoin Wallet" and none have the developer as Schildbach. The one to look for is "Bitcoin Wallet" by "Bitcoin Wallet Developers" whose URL includes the name schildbach.

Great resources here to help you select an individual wallet: https://bitcoin.org/en/choose-your-wallet
Truthfully, having your own wallet that works across Windows/Android/Chrome might be on the tricky side for beginners. If you don't mind a web-based wallet where it's controlled by another party, I'd suggest using Coinbase, Xapo, or Circle as the easiest way to get something cross-platform.
With a web-based wallet, you can still maintain a degree of control by keeping the majority of you bitcoin on a hardware wallet, a dedicated, offline computer that runs its own wallet, or a paper wallet, and then use the web-based wallet for smaller amounts.

Hi, this answer was moved to another question due to merging. Please kindly check and perhaps edit it to make it fit here.

This chart comparing all major desktop clients is pretty good,
and is well maintained by a bitcointalk regular:
 http://dre.natverk.org/compare.htm
Discussion about it here:
 https://bitcointalk.org/index.php?topic=83768.0
Nothing about e-wallets, though.

http://dre.natverk.org/compare.htm link is down :(

Personally I would recommend Electrum, it's a local wallet, doesn't require you to download the entire blockchain, has good features with regards to recoverability and accessibility.  Also you can run it in multiple locations at the same time (something the standard bitcoin wallet doesn't allow you to do), and you can also run it on your phone provided it's not an iPhone.
Other than this blockchain.com provide a good online wallet although I'm always cautious of these as you have to trust the company running the wallet not to make off with your coins. One place I would definitely suggest not leaving them is in exchange wallets, at least no more than you can afford to loose, and for when you make your cryptographic millions Cold Storage.

Running Electrum on a phone, you sure? Is there an Android or WindowsPhone version of Electrum?

This site is not really meant for product reviews or recommendations. Anything answered here might be outdated in a few months or years. And it might actually turn out to point to a scam site if the domain or whole wallet is taken over by evil people.
It's probably safer to only point to www.bitcoin.org and follow the steps there, one of which is choosing your wallet. Those people put a lot of effort into thoroughly reviewing and comparing wallets on points that matter greatly (i.e. security) and will try their best to exclude anything bad or remotely scammy.
Of course my initial warning still applies here too: let's hope that domain does not get hijacked or evil people sneak a bad wallet past their review.

Hi Jannes, I've merged a duplicate question to this one. Please kindly check whether your answer might need a tweak to fit here.

This is a project I discovered to be quite effective at evaluating the privacy provided by each wallet. Obviously in most cases, choosing a wallet is based on a trade-off between privacy/security and convenience and I found this particular repository to be useful at considering various aspects of a wallet.
Open Bitcoin Privacy Project
Various well-known developers and wallet maintainers also contribute to this project, so it should be fairly reliable. As a word of caution though, one must always be skeptical at all times when it comes to cryptocurrency.

The linked list doesn't seem to have been updated since 2016.

My recommendation would be to use bitcoin.org. It's the original bitcoin site, and it's also the best, IMO. They include almost all the wallets, from multisig to hardware ones.
But if you were to ask me, I would recommend you to narrow down your search to only hardware wallets, desktop/full wallets. The latter should be used in tandem with the cold storage method, where you host a client on an offline computer, sign a transaction there, then broadcast it using a computer connected to the internet.
Here is an tutorial and explanation for cold storage on the wiki.

My Recommendation would be the Trezor wallet, even though I own a Ledger HW.1.
Definitely one of the best wallets out there, it can take a physical beating, and has great software. It's cold storage for the pros! :)

Try https://blockchain.info/wallet it has Android and IOS clients. It is easiest client for begginer.

source: Stack Exchange

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authors: Валентин Нахуйвамэтонадо

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When making an altcoin copy of Bitcoin, where should one start?
In attempting to create a clone, a few things have to be considered... things like block time, reward, etc are often changed. What other things should be considered when messing with the source code?

Number of confirms for accepting mature coins from mining and transacting. Very few people understand that waiting for 6 confirms on the Bitcoin network is not equal to waiting for 6 confirms in Litecoin, for example.

You should study the current alt-coins world:

en.bitcoin.it: List of alternative cryptocurrencies
bitcointalk.org: List of all cryptocoins

The most interesting alt-coins today on my sight are:

Quarkcoin (QRK) blake, bmw, groestl, jh, keccak, skein
Primecoin (XPM) First non-hashcash proof-of-work in cryptocurrency, pure prime number based proof-of-work
Litecoin (LTC) scrypt

The fastest way to understand what must be changed is take a source bitcoin-0.6.3-linux.tar.gz and source of litecoin 60300.
Thereafter, extract both archives into two directories and simply diff -rHvn bitcoin litecoin.
Change the names of configuration files, number of ports, etc... And change the hash function, if you wish.
You surely will meet two common troubles:

Kill network by difficulty. Someone may come to your network with >50% of power, increase the difficulty and then disappear. After that, your network participants would found next block with BIG delay, which will break the stability of transactions, etc...
ASIC miner. Today, any gamer with a TOP video card can't mine, in the top pool, not even ONE Bitcoin for years, because of ASIC miners. What to say about a finding of block, solo-mining.

First can be solved, I think, by reinventing dependence on the difficulty by adding a dependency on Time. For example:

Next block must be with 10 zeroes in the start, but after one minute the
  number of zeroes would be decreased by one, at the second minute decrease
  this doorstep again, etc...

Second, the ASIC miner, may be conquered by the really hard hash algorithm. Look at the QRK: probably nobody will draw such circuit while the game isn't worth the candles. But here you'll meet next attack: someone may analyze the cascade of hashes and find a much easiest way to getting blocks.

You can observe the world of alt-coins and you will realize that nobody needs your new coin. There are about 30 very active alt-coins and about 100 in incipience. I predict: "In the next year this numbers would be multiplied by 10!": 300 active alt-coins with various difference from bitcoin and 1000 full clones, differing only by labels.
You could blow up the market with super innovation.
One of the most interesting and costly thing is traceability of money, on my sight. E.g. Look at zerocoin.
The second is a dying of mining. The market of bitcoin might plop in.

Edit: Also, there is rippled/xrp, sometimes ago it has become opensource.

https://github.com/ripple/rippled/
https://ripple.com/wiki/Introduction_to_Ripple_for_Bitcoiners

Also, look at granpa of ripple:

https://classic.ripplepay.com/login/

One day, surely, there will appear a child of bitcoin and ripple. Kind of crypto-money-mutant.

I leave here a little space for the future to add more interesting questions and answers.

How do I get the litecoin 60300 source?

Something like: cd /usr/src; git clone https://github.com/litecoin-project/litecoin; cd litecoin; git rebase 3aaa7ba5d05ff7ec35e2cd704e1e1b3da58b70b4;. You should download full bitcoin's and litecoin's gits.

Where did you come up with 3aaa7ba5d05ff7ec35e2cd704e1e1b3da58b70b4?

When you clone full litecoin's git repository,  you could check the log git log, there is record from Date: Fri Jun 29 13:42:04 2012 -0700: Change version to 0.6.3, thereafter going a couple of fixes. My current version of git for experiments with clones is: Date: Sun Apr 14 01:50:46 2013 -0700: with last log record: Do not warn about obsolete version.. It looks like a complete litecoin v.60300. Just try to rebase here and compare with bitcoin 0.6.3, you'll see that there is no so many differences between ltc and btc.

Please add a reference to Nxt ( www.thenxtcoin.com ), 2nd crypto-currency whose code doesn't descend from Bitcoin. It's an interesting concept: all coins have been pre-mined and no more will ever be, you earn interest just by holding some Nxt (receiving a share of the transaction fees paid by others) which is proportional to how many Nxt coins you have.

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text:
Will transaction confirmation time be reduced as the network size increases?
Right now it takes 6 confirmations, which takes about an hour to verify a transaction. Will the rate at which transactions confirm become faster over time?

No. The average time per confirmation will always be about 10 minutes (but it's possible that the variance will be lower in the future). And the number of confirmations required to prevent double-spending by an agent with a given hashrate will also not change (6 is an arbitrary number reflecting a "low enough" probability for someone with a "high enough" hashrate).
What will change is services to bridge the gap. There will be split-key eWallets which cannot steal your money on one hand, and can have trusted green addresses on the other; and there will be insurance agents such as https://zipconf.com/ that absorb confirmation risk based on their model of the probabilities of double-spending.

In the future mining rewards will be based on transaction fees, which gradually increase while waiting for a block to be found. If miners wait until fees accumulate before doing active work, there will be less variance in the time it takes to find a block.

Isn't it true that these "insurance agents" could easily be singled out and targeted by double-spending attackers? In other words, they would crash and go near-bankrupt the moment someone decides to attack them right?

@Pacerier: No, because their risk management strategy will be adaptive. They will only have a certain amount of coins at risk at any time. If they're being targeted for double-spending they will quickly increase their parameters to make further attacks more difficult. Attackers have limited ability to attack (based on their hashrate) and the insurer's fees will depend on the probability of double-spending success. Also, the insurer can work completely behind the scenes, so the attacker would not know the specific entity to attack.

there's no way the insurer could hide the IP addresses of its nodes right? Thus, the attacker(s) only have to ensure that they coordinated attack network is stationed near the insurer's nodes to completely bring the insurer's business to a grinding halt isn't it?

The attacker doesn't need to know there even is an insurer. He gets an address from the business and he doesn't know if there is an insurer who is really in control of it. Tor could be used to hide the IP address. Network topology attacks are different from hashrate attacks. The insurer would do well to have access to several nodes around the globe to ensure an accurate view of the blockchain. Anyway, even if there are some potential vulnerabilities to explore, this is getting beyond the scope of SE comments.

Actually the amount of confirmations is seperate from verification. The more confirmations a transaction has the more certain a transaction is. The point where you say it is "verified" is simply the point where you trust it sufficiently.
When do you trust it? For a person this it's a feeling in your underbelly. How fishy is a certain deal? How trustworthy is the person transacting? How are his/her technical capabilities? How gullible is that person? For companies the equation is more exact, but can still be chosen. Can we take the loss if this was a trick? What is the chance that a transaction is fake after X confirmations and would it be more profitable to have someone cheat us every so often, if it makes our service faster? The perfect one is "Would an attack have been more expensive than the value of the transactions in the block in which they were created and those after?".
The notion of six is certain is a fallacy. However after the third confirmation this is a true 51% attack which is fairly hard to do. So six is abundantly secure.
http://bitcoinwatch.com/ now estimates the PetaFLOPS within the network's capabilities to be nearly 150. In January renting 240 Teraflops came at a price of 1280$ an hour. To get 75% of the current network's hashrate for half an hour one would have to spent 150000/240*1280*.5 = 400 000 USD's. So unless you're dealing with fairly huge numbers, 3 confirmations suffice. Edit: because the hash complexity doesn't grow every block it is 3 confirmations or 35 minutes, whichever takes longer. This should dampen the attacker's ability to burst a few blocks within a short period of time. The additional 5 to ensure sync. If you want that 400k limit you require an additional block to ensure the previous 3 were okay.

The gambling site satoshiDICE has an interesting take on this.  They accept bets immediately, with zero confirmations, and pay out immediately if you win.  This may seem risky, but there's a trick:
Part of your winnings are paid with the amount you sent as your bet.  So if your bet was a double spend, and ends up not making it into the blockchain then neither do your winnings.
I thought that was quite a clever take on the whole question of how many confirmations is enough.
Oh, and to answer the question, each confirmation takes 10 minutes by design.  If confirmations start coming faster than every 10 minutes then the network adjusts the difficulty of finding a block to slow down the confirmation rate.  Similarly if confirmations are taking longer than 10 minutes then the network reduces the difficulty of finding blocks.
It may be in time that people start trusting transactions with 4 or 5 confirmations, or maybe they're get more cautious and start waiting for 10 confirmations.  But that's nothing to do with the Bitcoin network - that's just people and their perception of risk vs. reward.

I don't quite get this... if you were trying to double spend on satoshi dice, you'd only do it if you lost.  How does paying winnings out of the bet prevent the loser from double-spending his losses?

@Brian Clever question.. Anybody got an idea?

No, it probably won't. 6 confirmations, or 1 hour is considered a standard amount of time required for any Bitcoin-like crypto currency to ensure a transaction will not be reversed. The time to generate a Block will not change without changing the protocol (which is unlikely to happen), so one would still require an hour to generate those 6 confirmations.
However, even now you can see 0 confirmations transactions appearing in your client in seconds, and it is only up to you to decide when you consider that money secure. Recently 4 blocks were replaced by a miner with a big amount of hash power, meaning transactions in those abandoned blocks were vulnerable to double-spend attacks. However, such cases are rare.
Moreover, even right now some people are working hard on making the confirmation problems less bothersome to the users. Some want to establish some assurance from pools that would promise to include a transaction in their next block, other build bank-like systems that would process internal transactions without the need for blocks (currently you can do that between MtGox's accounts for example).
Generally, as a user one normally doesn't need faster transaction confirmations as double-spend attacks are not that frequent (not to mention detectable within a couple seconds in most cases) and one rarely needs to provide something to the receiver on the spot. It is mostly an issue for micropayment trasaction providers that need to clear an operation within seconds, not being able to wait even for 1 confirmation.

Could you provide a source for the 4 replaced blocks? It seems like a fairly huge achievement.

@Lodewijk updated the answer.


text:
What financial instruments are under development for Bitcoin?
I'm thinking here specifically of instruments that take a Bitcoin-like approach to trusted parties, eliminating them wherever possible and typically built with Bitcoin as their platform.  (As opposed to simply having a real-world trusted entity issue a Bitcoin-containing or Bitcoin-related financial instrument in the traditional method).
Financial instruments include things like bonds, stocks, contracts, additional currencies, etc.
For example, I know jgarzik was working on smartcoin for a while (has development stopped?) and there are things like this you can do with coloured coins.  Can anyone offer some insight on what is actually being developed re: these and other approaches, and especially what has reached an implemented, usable level?

not sure if this is what your looking for, but ripple is doing some cool things along these lines

Does Ripple actually add any new financial instruments other than currencies?  In general, though, I'm talking about development which uses Bitcoin as the platform.

Lots of people that we know about and probably many more that we don't know about are developing a diversity of financial instruments for bitcoin. What instruments exactly will depend on your definition of instrument.
Here is an interesting one:
cvToken:
An effort to stabilize the bitcoin price by pegging a token backed by a basket of commodities to it.

Yeah, I heard about this at the Bitcoin conference.  Although I think they are trying to stabilise the token, not the bitcoin price (can someone correct me on that?)


text:
How do I switch from Bitcoin-QT to a lighter, faster (SPV) Bitcoin client?
So, keeping up to date with the blockchain is getting ridiculous in Bitcoin-QT, especially on my laptop.  If I leave it off or away from the internet for even a short period of time, it takes forever to catch up.
But, fortunately, the Bitcoin network allows for a simpler model, called Simplified Payment Verification (or SPV) mode where only the headers of blocks are needed.  In addition, the Bitcoin network has recently been updated to support bloom filtering so that a client only needs to download the transactions that it is interested in (plus some margin for privacy).
First question:  Is there a client capable of importing my Bitcoin-QT wallet that supports these two options? (and preferably has a light resource footprint if I'm not asking too much)
And secondly, if so, how can I accomplish the switch with minimal pain?

From my experience, your solution is the MultiBit Wallet software - it should satisfy all your requirements: https://multibit.org/index.html
I use it on a regular basis and found it satisfying, and also have the possibility of storing more than one wallet, you should give it a try.
Cheers.

Could you explain how one switches a wallet over to multibit?

The least painful way is to let go of your old wallet, as long as you know that nothing else will be ever coming to you on any of those addresses. Simply start the new client and send your balance to one if its new addresses.
If you must hold onto your old addresses, look for a client that can import the Bitcoin-Qt exports. I believe that MultiBit can do this.

You've hit the nail on the head--this wallet holds addresses that are widely distributed in non-updateable locations and may continue receiving deposits.  How does one go about importing into MultiBit?

To import into multibit, first create an new wallet in multibit. Then choose "Export private keys" and don't set a password. Edit the .key file and enter your real private key instead. Save and import back in to multibit.


text:
Would it be possible to patent Bitcoin?
Bitcoin utilizes a proof-of-work mechanism to assure against double-spending, as well as providing an example opensource implementation.  However, some countries allow software patents, which could mean that one person/company has the ability to suddenly prevent the legal use of Satoshi Nakamoto's Bitcoin algorithms.
Are these Bitcoin algorithms complex enough to qualify for being patentable, and if so, in what countries might such patents be granted?  Does this pose a significant legal risk for users of Bitcoin?

To claim a patent you must be able to prove against contest that you invented the device, and have a working example that if built to the specs provided, runs.
As it was this Satoshi who invented bitcoin, and there are prior examples of a digital currency, it would be very hard for any one person to claim a patent so far after the fact. Some one could try, but the patent industry is built to make it hard to write a patent, easy to contest. Admitedly many companies do just that and are good at it, but anyone patenting bitcoin would have a hell of a time proving first invent.

Given that there are a few details such as known public key for Satoshi, couldn't he/she prove invention and thus patent it? While given the little we know about Satoshi, it seems unlikely; what if for some reason Satoshi decided the whole thing had not turned out as desired and wished to reign it in? Also, Satoshi may have unknowingly infringed some patents. It seems relevant to the question to ask 'what could such a patent holder do'?

@JulianNoble AFAIK you have a certain grace period(a year or so) for filing a patent after publishing what you want to patent. So unless he already filed the patent, it should be too late now.

It's in no way easy to contest a patent. It's a quite expensive process.

It would be impossible to patent the Bitcoin-protocol as a whole, but it is possible to patent new codes before integrating them into the Bitcoin protocol.
A good example are the patents made by Blockstream. 2015/2016
US Patent : US20160358165A1
US Patent : US20160330034A1
So imagine this new codes are integrated in the Bitcoin protocol, and somebody later wants to do a fork of the new bitcoin protocol. Blockstream know has the IP ownership to this new codes inside the bitcoin protocol. They can claim a payment for licence or forbit the fork. It depents on Blockstream if they want to use this patents to make money.

While what @Evil has said could be theoretically true, in practice often happens that random people patent random stuff "just because they can", and then it will have to be settled on court (with all the related problems).

While true, I imagine it would be fairly difficult for someone besides Satashi Nakamoto to make even even a somewhat plausible claim of inventorship since he the original description of Bitcoin is publicly available.

@Michael: sadly it doesn't matter if it plausible or even patentable, they can file it anyway, and it will be accepted anyway.

Well yes they can file even the most ridiculous of patents, but are you telling me that the patent examiners won't even bother doing a simple Google search to attempt to verify novelty?

@Michael: sadly, yes.

while its true that when filing a patent, the examiners do little to know research, and don't really care. A challenged patent is looked at closely by many parties, and frequently has to be decided fairly by a judge.

The Bitcoin algorithm is a mathematical equation with the block as the answer to the problem. Showing proof-of-work is the foundation of all math and science. Ask any math teacher. Whether or not it is to assure against double spending is a matter of (popular) opinion and is not an absolute 100% certainty. If a particular algorithm is somehow patented, then it would require a hard fork of the Bitcoin block chain to slightly change the algorithm. There are as many opinions about how Bitcoin should work as there are programmers and no shortage of ways it can be forked if absolutely necessary.

As long as the Bitcoin project is open source it would be very hard to claim a copyright on that code which is freely available for copying.
Now if someone wanted to copyright a derivative work then that is possible.

Copyright has nothing to do with patents.


text:
How can you tell how many users Bitcoin has?
Impossible to answer accurately, but I suppose one could come up with educated guesses and ballpark figures from the number of nodes on the network, or number of users on popular wallet services.

because any answer to this question will be out of date as soon as it's answered, it's a classic example of a question only relevant to a "specific moment in time." I suggest you edit it to be something more universal, like "How can you tell how many users Bitcoin has?" and a moderator will reopen it.

@Jeol - so why close preemtevly when you can just suggest edits or even edit.

I suppose the total number of receiving addresses is an upper bound for the user number (not a very tight one, though).

Updated with user count of r/bitcoin and Bitcointalk

Due to the nature of Bitcoin there is no precise answer to this question. However, this site displays some statistics on the number of nodes in the network over time: http://bitcoinstatus.rowit.co.uk/

Check out my answer to this question about geo data.
In fact, I would recommend creating one question about "How can you get statistics about Bitcoin users / clients" instead of asking about every different slicing of the data.
Is there data on the geographic distribution of bitcoin users?
http://www.reddit.com/r/bitcoin just crossed 10,000 users a few days ago (Sep 2012), to help you get some estimate.
https://bitcointalk.org/index.php?action=stats - Bitcointalk currently has 64,175 users.

The challenge is to merge different addresses that all correspond to the same user. Since bitcoin isn't quite as anonymous as it's cracked up to be, this isn't totally impossible to do.
One way to do it is to merge all addresses that contribute inputs to a single transaction. That's based on an assumption, but it's pretty reasonable one.
Another way: connect your computer to all other Bitcoin nodes. Whenever you see a transaction broadcast that you haven't seen before, log it and the IP it's coming from. Since you're connected to all nodes, that is the sender's IP (unless they're anonymizing with Tor or some such).
These approaches are used in a couple of papers:
http://anonymity-in-bitcoin.blogspot.com/2011/07/bitcoin-is-not-anonymous.html
http://eprint.iacr.org/2012/584.pdf
The estimates from those papers aren't totally current, but you could extrapolate. Ron and Shamir (2012) count 3,730,218 addresses and 2,460,814 "entities" (conservative estimate of users). So multiply current addresses by about 1.5 for a ballpark estimate.


text:
Bitcoin-Qt wallet shows outgoing transaction as "Offline (0 confirmations)"
What is the meaning of a transaction status of "Offline (0 confirmations)" as opposed to "Unconfirmed (0 confirmations)" ?
Does it mean that the transaction has not even been sent to the network yet?
If so, why would that happen, and can I force it to retry?
The wallet is online (13 active connections to the network), but out-of-sync (catching up very slowly, last received block was 1100 days ago).

Update: I have restarted Bitcoin-Qt. Now it says "Unconfirmed" (no longer "offline"). But the transaction cannot be found at blockchain.info. So has it really been sent?

Offline means that the transaction hasn't been sent to the network, that is, it's not in the memory pool of any other node.
Unconfirmed means that the transaction has been sent to the network and exists in the memory pools of many other nodes.
If the wallet is out-of-sync, that would be the reason it's got 0 confirmations. Even if you did have a confirmation, your node wouldn't know it since the transaction would be in one of the newest blocks.
If the transaction is not on blockchain.info, there's a very good chance that it hasn't been sent. You should probably resend it using the instructions found here.

The instructions assume that blockchain.info already knows about my transaction. How do I get the binary transaction out of Bitcoin-Qt?

you can use the getrawtransaction command. It should be in your bitcoin-qt's mempool.

Thanks, I was able to getrawtransaction and then paste that into blockchain.info.


text:
Does Bitcoin wallet encryption also protect my sending and receiving addresses?
Bitcoin wallet encryption makes sure (by encrypting the private keys with a passphrase) that someone who finds your computer or your Dropbox or your backup drive (including wallet.dat) cannot spend your coins.
Does this also protect my receiving addresses (which I may not want to be associated with to protect my pseudonymity, and finding them in my wallet would remove plausible deniability)? And how about the aliases I have associated to sending addresses, which might breach confidentiality with my business partners?
If not, what additional steps do I need to take?

Probably related: http://bitcoin.stackexchange.com/questions/2150/where-are-the-receiving-and-sending-address-descriptions-stored

Clearly your receiving addresses, your sending addresses and their associated aliases are readily available without the passphrase to your wallet as they are visible upon opening the Bitcoin client without entering the passphrase.
It's perhaps also worth noting that even if your wallet is encrypted, a successful attacker who has a copy of your wallet could install a keystroke logger to obtain your passphrase.
This would seem more likely to happen when your computer is compromised through installing a trojan etc than if someone physically found say a lost notebook PC (for which the attacker would need to install the keystroke-logging software & remote access software, and then give you your computer back so you would type in the passphrase next time you wanted to send coins!)
Sorry, I don't know where the sending and receiving address descriptions are stored, so I don't know how to protect them - hopefully someone else can answer that.

Updated the question to show that people can find wallet.dat without getting to the computer itself. +1 for pointing that out.

They are stored in wallet.dat, so putting that file in a Truecrypt volume could be a step towards securing them.


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Given the current situation, what currently available Bitcoin clients are the most likely to follow the longest chain one month from now?
I am completely lost with the various BIPs and what exactly every client implements. So given the current situation as of July 2017, what currently available Bitcoin clients are the most likely to follow the longest chain by end of August?

What do you mean by "longest chain"? All Bitcoin nodes always follow the "longest valid chain". The past disputes are about what to consider "valid".

@Murch: every client follows the longest valid change according to their own rules. However, since a hard fork is likely, their will be multiple valid chains for different clients. I'm asking what the longest one will be, or more specifically, which client(s) will follow it.

What does 'longest chain' mean if you don't qualify according to which validity rules?

We don't know what will happen, therefore it is hard to say which client will be on "the longest chain".

Core is scool with bip141, so it will follow that.
Segwit2x hard fork will be using BTC1.
USAF could hard fork as well so that client will be for that chain.
BItmain's BitcoinABC will have their own client (I'm not sure what that client will be/is called).

Well I was hoping that with the support expressed in blocks, someone who understands what is going might be able to make an educated guess, or at least give some information about the likeliness that each chain will "win".

What does 'winning' mean? The point of a fork is that there will be two chains. According to Bitcoin nodes, the Bitcoin chain will one. According to S2X nodes, the S2X chain will win.


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Who has this many BTC?
http://blockchain.info/address/1VayNert3x1KzbpzMGt2qdqrAThiRovi8
I don't understand who could possibly have this many BTC.

That is DeepBit's payout address. Whenever DeepBit pays its miners, it sends one transaction per miner, and each transaction comes from 1VayNert and sends change back to 1VayNert. The change from these thousands of small transactions adds up to create huge "total BTC received" amounts. 1VayNert has never actually contained anywhere near 10 million BTC -- that's just how much BTC it has sent to itself in change from transactions.

The "Final Balance" for that address is only a bit over 2000BTC, so it's not actually a very high figure for how much they own.  As theymos says, the "Total Received" figure is something else; it's a measure of volume sent through that address, and can count the same bitcoins many times over.

Here's a chart showing the balance at that address over time.  It once nearly reached 12,000 BTC.

According to this forum topic it belongs to DeepBit (currently the largest mining pool)


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How long does it take to receive bitcoins?
I bought 1.25 BTC but after 2 days I see nothing. What is wrong?
This is the transaction.
Also, I went to freebitcoins.appspot.com, since they claim thay they give for free 0.005 bitcoins per visitor. I did everything correct and the site said that I could see the transaction at freebitcoins.appspot.com/recent_sends.
But when I clicked on my transaction, it said: No such transaction
http://blockexplorer.com/tx/1eaf91e7d4ae3a8f976eaa346f4332d8bfd999d209ef899612e5b2995db0eeb9
Please guys tell me what is wrong?

If you see the transactions in block explorer, you have the Bitcoins. Block explorer is showing you the actual live network data.

If you know the transaction ID but it doesn't appear in block explorer, it means this is a floating transaction which hasn't been included in a block yet. This transaction already appears in BE at the time I'm writing this. For a list of known floating transactions you can use for example http://bitcoincharts.com/bitcoin/ .

Also, search on Blockchain.info will show transactions that have not yet made it into a block.

You should check the following:

Are you sure you entered the right address to receive the Bitcoins?

If the address is not correct, the coins are lost

Did your Bitcoin client download all the blocks in the chain? (>150000)

If not, you need to let it run for awhile, until it downloads all the blocks, making sure that you have a couple connections and the block number is slowly increasing in your client application

Did you allow ample time after downloading the bitcoin app to allow the entire block chain to be downloaded from within the app? If not, then the most recent transaction wont be visible to you.


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New User, New Wallet
I recently purchased some bitcoins, which were sent via coinapult to my cell phone.  I received a text for the amount with a link to an online wallet (apparently not a true wallet but just an account within a larger wallet).  I would like to have my own wallet.  I’ve downloaded the bitcoin wallet program (for windows) from this website.  (bitcoin-qt) version 0.6.2-win32.  When I open this program it claims to be “synchronizing with network” a certain number of “blocks”.  In the “received  coins” tab is listed an address.  Using my coinapult via the link provided on my smartphone I sent a bitcoin to the listed address.  However I see no evidence it was received.  Do I need to wait for the synchronizing process to complete to send bitcoins to this wallet?

@luke Welcome to the Bitcoin StackExchange! Your question has been answered here before: http://bitcoin.stackexchange.com/questions/91/how-do-you-obtain-bitcoins

Using the default client (which it appears you are) transactions received while the client is online will usually appear immediately but transactions which occur while the client is offline will not appear until the block containing them is downloaded. Based on your description this appears to be what has happened, so your transaction should show up whenever that particular block downloads.
You could also try punching your address into http://blockchain.info and you should be able to see your transaction as well as what block contains it.

You can send Bitcoins to a wallet even without being synchronised, but you will most likely only see them appear once you do get synchronised. If everything goes well (it should), your address will be credited and the record will be stored in the block chain, allowing you to retrieve it upon synchronisation.

Lets hope, its been 2 hours and its just over half the blocks have been synchronized.

The synchronisation is slow, and gets slower towards the end, so having half the blocks doesn't mean you're half way through.  (Recent blocks are bigger than early blocks, since the Bitcoin network is used more now than a couple of years ago, and the very newest blocks are subject to more thorough checking than old blocks). You only have to do the full synchronisation once though.

"You only have to do the full synchronisation once though.". Well, if you turn your client off for a week or so, you'll be spending some time catching up again.

@Thilo Yes, but it will be nowhere near as long as synchronising 3,5 years of blocks...

Over the night my computer froze and became unresponsive.  I do not think synchonizing process has finished.  After restarting my computer I cannot even open the wallet on my labtop. It gives me an error loading message whenever I attempt to open it.  It spent at least 12 hours synchronizing and did not finish, even though my web connection is fine.

@Dave Probably means some file became corrupt. You'll have to delete all your files from Bitcoin data directory (asides the wallet.dat, that file you should never delete!) and start Bitcoin again, which means you'll have to synchronise again.
You could always look into some eWallets, which will let you use Bitcoins without the need to synchronize, ever. Alternatively, there are some lite clients that don't require as much synchronization...

Ok in the bitcoin folder that downloaded from this site there are 4 icons and 2 folders.  The folders are "daemon" and "src".  The icons are bitcoin-qt, license, readme,(last two are just notpad text documents) and uninstall. Whenever I click to open bitcoin, it errors.  Are you saying I should delete all the icons except the bitcoin-qt?  If I did would that mean it should start or should I simple redownload the package?  If I did that wouldnt it overrite the current one?  sorry Im just not that fluent in computers.

@Dave That's Bitcoin installation folder, while the data folder you can find here - http://bitcoin.stackexchange.com/a/4007/323 (probably C:\Users\YourUserName\Appdata\Roaming\Bitcoin). If it has "wallet.dat" file, you're at the right place.

Yeah, nothing is working.  I cannot get bitcoin to open at all let alone begin the synchronizing process again.  I just wont even open.

I've redownloaded the windows wallet setup.  It downloads fine but as soon as you run it, it fails to open, just as previously. The original wallet is still on my desktop.

@Dave You don't need to delete the CLIENT (in Program Files), but the files in the Bitcoin DATA FOLDER (Appdata\Roaming\Bitcoin), except the wallet.dat.

I deleted everything in the date folder except the wallet.  However the wallet still will not run.  I redownloaded the windows version, however it will not creat a new folder, it simply fails to run after its downloaded.

@Dave Hmm, that is strange. If you move the Wallet out of the data folder to some other safe place and run Bitcoin, does it work? Have you uninstalled and reinstalled the client? If it is just the wallet that doesn't let Bitcoin run, you might want to redeem it in places like MtGox. If all of that doesn't help, you ought to start a new question on this problem.


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Downloading of blockchain failed
I’ve been attempting to set up my own wallet, but am having difficulties.  Last week I began installing the standard Bitcoin client.
When I first attempted I got to the process of downloading the blockchain.  My computer ran for about 36 hours until the process failed.  I asked on the message boards and they said there may have been some corrupted data.  I attempted to re download the blockchain, but when I reinstall Bitcoin, I now get a failed to initialize message.  I deleted the original files (except the wallet file) and still get a failed message when Bitcoin starts.  It's getting pretty frustrating.  I sent 1 bitcoin to the first address I created (though it had not yet and never did finish downloading the block chain).  Would deleting the wallet allow me to start over?

Operating system & Version?  Also, assuming this is the Bitcoin.org client, which version?
This wouldn't be a permissions issue, by chance?

If you sent a coin there, of course you need to keep the wallet itself or you won't be able to claim that coin.
You may delete and re-download the blockchain, though.
Or you can try to open the wallet with another client.

I have attempted that several times.  I've put the wallet on a flash drive and unistalled bitcoin all together.  I've restarted my computer and done a program search to confirm that there are not bitcoin programs on my computer.  However once the wallet begins to run after about 10 seconds (before the blocking process begins) I get the following message "error loading blkindex.dat"

I've no idea what the "blocking process" is. Are you sure you sent bitcoins to that wallet? How did you do that?

When I first downloaded the program it began downloading the block chain.  I let it run for 36 hours, at which point it failed.  I was told it would need to complete the chain one time, however after it failed no subsiquent attempts to open a wallet have succeded.  Once you get to the point where it says "completing the bitcoin setup window" and press finish I see the wallet icon saying "loading block index" and after about 10 seconds a "error loading blkindex.dat" message after which the program closes


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My wallet won't load because it says it contained a duplicate transaction. Are my coins lost forever or can i load it some other way?
Question pretty much says my dilemma. Wallet won't load due to a "duplicate transaction" which I thought could not happen. I use multibit btw, if that helps. Please tell me I can load my wallet somehow.

Because this relates to Multibit rather than the standard client, I don't think it's a duplicate question. You might like to take a look at the information regarding the same issue for the standard client though: http://bitcoin.stackexchange.com/q/3654/516 http://bitcoin.stackexchange.com/q/4152/516

SHould have mentioned, I didn't spend bitcoin, I was recieving it.

This was a bug that was fixed in v0.4.1 (26 June 2012) so I presume you are running an earlier version. If you download the latest version from multibit.org your wallet should load ok.
Sorry for the inconvenience.


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Why would we ever need 10k new addresses in average per day?
Generally speaking, the address space of Bitcoin seems to be sufficiently large to make it unlikely that a hash collision will ever occur (see below).
Pacerier stated in a comment on Is it possible to brute force bitcoin address creation in order to steal money? that we'd "want Bitcoin to scale to [...] 10b people, each generating 10k different addresses a day, that's 100 trillion addresses created daily." He followed up with "10k may be a severe underestimation".
100 trillion is 10^14, so if we kept up that pace, we'd have used one address per satoshi after 21 days. I am confused as to what might be the reasons for users to need 10k addresses per day.
Please explain: Why does it seem likely that we will need such a large number of new addresses each day? In what scenario would each user in average need 10k new addresses per day?

Total number of satoshis:

At one address for each satoshi that could be ever in existence (2.1*10^15), with the giant address space of 2^160 possible addresses, the simple approximation of the Birthday paradoxon, which works well for probabilities less than or equal to 0.5...

... tells us that the chance of single hash collision occurring is still pretty small: 1.508*10^(-18).

I see an issue with using satoshis as a limiting factor in future hypotheticals. It's been suggested that if it were ever deemed useful/necessary, the satoshi could easily be split further. (although by that point, hypothetically, we might've moved to longer addresses to avoid just this problem)

I would say before we are dealing thousands of microtransactions per day, which I still consider to be far off, is the idea of people and corporations using vanity addresses. Let's just say that I want all my addresses to start with Mark (or as close to mark as possible, e.g. for bitcoin would be 1mark and for litecoin would be Lmark and so on).
Since there is no way to start with an address including, say 1mark, and reverse to find the private key (an assumption on which mining, password hashing, and many other security protocols are based on); I will have to do the inverse: generate a random private key, create a public key, and check if this public key meets my criteria. If the address I generated starts with 1mark then I will add it to my wallet, otherwise I will throw out this private key and try again until I find my address.
Bitcoin and it's derivatives do not allow certain characters in public keys as to avoid confusion. I believe these restricted characters are: number 0 and capital O, number 1 and lowercase l (except for the first character in a coin address). This means that I have 58 usable characters (26 UPPERCASE letters + 26 lowercase letters + 10 numbers - 4 unusable characters in these sets). I do not believe there are more but someone please correct me if I am wrong :)
If there are 58 usable characters for an address, and let's say I am very concerned about the capitalization of my name (i.e. it needs to be 1mark, not 1MaRK or any other permutation with capitalization), the average amount of addresses I will need to generate to find an address begining in 1mark would be 58^4, or 11,316,496. If I didn't care about the capitalizataion of my name it could be as low as 707,281 addresses generated to find an address which begins with my name. That being said, I have a pretty short name, someone name Satoshi will need many more hashes to get his name as a vanity address.
If the water company is using vanity addresses as well, (e.g. 1water) to help their customers differentiate their charges or for any other reason, this increases by the amount of vanity addresses they use per day.
I would use a vanity address generator (see disclaimer) to do this currently, I imagine it will likely built in to standard wallet software at some point, since it is a nice novel feature and allows for more custom firstbits (short identifiers for bitcoin addresses, more information on firstbits can be found here https://en.bitcoin.it/wiki/Firstbits ).
Disclaimer: be careful how you generate a vanity address, currently the best method is to use VanityGen (more info here: https://en.bitcoin.it/wiki/Vanitygen ). Please read up on the possible issues with a vanity address generator and make sure to do so securely if you intend to use a vanity address to save any significant amount of coins (e.g. make sure that the developer can not get access to your private key during or after creation, by running vanitygen on a live usb without connecting to the internet).

Thanks, I did not intend to replace your answer, which is very good and to the point, but I wanted to chime in about vanity addresses (with explanation), which did not fit in a comment :)

Very interesting points, however if the private keys for the misses on vanity address generation are discarded, the number of addresses in use is actually no greater than if they just used a random address. The chances of getting a hash collision with a vanity address might be greater though. If all tries were retained, I could see how that would cause a huge number of addresses being used everyday.


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What's causing P2Pool's bad luck?
While looking at the current pool luck chart on p2pool.info, I noticed that the pool as a whole seems to slowly deviate from the predicted rate of finding blocks.

From the other chart it appears that it is consistently underperforming as of 3 weeks ago.

Is there a good reason or is it just a fluke in the probabilities of finding a block?

the graph across all time shows that it has deviated much more than that for much longer durations of time. I wouldn't worry about the current fluke

This looks like plain old bad luck.
P2pool is a small pool and 3 weeks is a short time. With current hashpower at pools this is like measuring BTCGuild for less than 12 hours. BTCGuild can have bad luck for 12 hours, and P2pool can have bad luck for 3 weeks.
That said, all pools underperform on average when compared to a simple expected income. That's because of orphaned blocks, typically 1 to 2 percent. And if you count stale/rejected shares in the hashrate, then it will underperform even more. But if income from transaction fees is not included in that expected average, then that may even out the orphans and stale work.


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Standing Orders, Is it possible with Bitcoins?
Is there a service out there, or is there any intention to integrate Standing Order type transactions into the client ? (Every 30 days transfer 0.2BTC to a specific address for example).

possible duplicate: How could recurring payments be implemented?

One way to accomplish this today is to run Bitcoin with the -server switch. Then, create a cron job (Linux) or scheduled task (Windows) that calls bitcoind with the proper arguments. Something like...
bitcoind sendtoaddress <address> <amount> <comment>

The up side of this method is that you can run a lot of different commands this way. See the wiki for a full list of available RPC calls.

I don't think the client could be relied on for this as it would need to be running all the time.
So you would need a 3rd party e-wallet service.
Technically this would be very easy to do.


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If I have a public wallet address can I calculate its other wallet addresses?
Lets say someone else generates 100 bitcoin addresses using the same private key.  If know one of the public addresses, can I deduce the other 99 public addresses?

Public keys are generated from a Private key in a one-way function. Public and private keys have a 1-to-1 relationship. A given private key can only generate one public key.
However, as specified in BIP 32, extended keys can be used to derive child keys (public keys). An extended private key (xprv) can derive many child private keys, each of which can derive a single public key.
This child key derivation (CKD) function is a one-way function, so child keys cannot be used to calculate their parents. Nor can child keys be used to calculate their sibling public keys.
Check out this article on wallets and public/private keys for more info and a visual explanation: https://river.com/learn/terms/h/hd-wallet/
Check out BIP 32, which has some useful graphics: https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki

Relationship between private and publiic keys is ( in practicality ) unidirectional and 1:1 so given an algorithm; a private key will always, generate the same public key.
There's an advanced concept, that has to do with your question and is deterministic wallets. Here private keys are created from a seed and there are scenarios where you could guess them from knowing one; but you would need to know the private key, not the public.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Automatically buying bitcoins from SEPA deposit
I'd like to buy bitcoins via SEPA deposit automatically with a recurring schedule. To specify this with an example, I would like to purchase bitcoins for 100 EUR each month, at the current market rate, without manual intervention. For this, I can set up a recurring payment at my bank to a SEPA bank account. The manual way to do this at Bitstamp would be:

Start SEPA deposit at Bitstamp for 100 EUR.
Make a bank transfer to the given account with the given message.
Wait for funds to appear at Bitstamp.
Use instant order to purchase bitcoin for 100 EUR (converted to dollars).
Wait for the transaction to complete (may take days if market fluctuates).
Withdraw bitcoin from Bitstamp to a given address.

I am not bound to a single exchange, any one of them will do as long as they roughly follow the current market. I am not afraid to run a server, or to create my own program using an API to do this. However, I am not willing to use screen scraping, because I would wish for this to run with minimal intervention and such an approach would seem too error prone. I am also obviously not able to affect my bank, so the best I can do is to have a recurring payment with a fixed message/reference number each month.
Is there an exchange or combination of services that will let achieve the above automatically?

Sorry, not willing to have an invidual do it for me either. Thank you for the offer, though.

Xapo allows you to do this.
When buying bitcoins with them you get a unique code which has to be added to the SEPA transfer. Any funds received with that code are automatically converted to BTC and added to your wallet, indifferent of the amount or from what account it is coming from.
Now I get to think of it I see a great opportunity for a service which allows you to send a SEPA transfer with a bitcoin address in the message field, automatically converting the fiat currency into BTC and transferring it to bitcoin address. Transfers with faulty addresses could be bounced, and like Xapo a 1% fee could make it worthwhile...

Please don't post affiliate links.

Bitstamp does not require a unique code in every SEPA deposit. They require the same code everytime you send euros. So you can setup a recurring payment to your account. Maybe the first time, when requesting the SEPA deposit, type in the comment that you will be making monthly deposits.
Then write a program that checks the EUR balance daily and buys bitcoins for you. This should be pretty straightforward.
Bitstamp only offers limit orders through their API. If you want to speed up the buy order, set your price a few percent above the market price.
Good luck!

Unfortunately, I asked Bitstamp about this use case via their support, and they said you are not supposed to send money via recurring payments. So, while technically possible, they do not allow this (or atleast did not, when I asked).

There is a website called  Bitcoin Magnet that does exactly what you require. Check them out, they have good reviews. They convert a bank transfer containing your reference code into bitcoin (using Bitstamp) and send it automatically to your desired bitcoin address. You can therefore set up a standing order to buy on a regular basis. UK only.

Great! Shame about being UK only. Hopefully someone does the same for SEPA in general.

The link is dead.

And what's your question?
If you can use API, do it. Else, simulate browsing the website: get html code to string in your program, then search for some html markup e.g.
321.24243 USD
 and fetch proper data, then send it in proper forms. You can use php, curl, wget, Apache Commons httpClient or any similar tools/libs.

I want a solution to my problem. I explicitly said that I do not wish to use screen scraping (which means parsing the HTML markup and emulating a browser). Also, Bitstamp API does not seem to support all the operations, nor does it allow deposits without a unique "message", which does not interface well with recurring payments. So, how do I do this?

It's not possible then.

No? No single exchange in the world offers this? No combination of exchanges can be used to achieve this? No invidual is willing to work as a proxy for this? Note, I am not mandating the use of Bitstamp, that was just an example.


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Pricing TradeHill compared to MTGox
I've just launched a trading app that trades on MTGox and TradeHill.
I'm noticing something strange on TradeHill though. Basically I get my quote and place an order directly after. The order never gets filled as the price has already moved. I don't notice this on MTGox which is a surprise because there are higher volumes there and one would think that the price would move quicker there. Also, if I log on to TradeHill myself and fill the order form manually using the quoted price my order has been filled by the time my browser reloads the page?
Have any of you guys noticed this? These orders are being made when there is an arbitrage opporunity between MTGox and TradeHill.. Could this be the reason for the momentary volatility.. i.e. lot's of bots place orders to exploit the difference?
Any ideas on this appreciated.
Thanks :)
P.S. I forgot to mention that there is often a pretty large spread between bids/asks on TradeHill.
EDIT:
I'm using the ticker API to grab buy/sell quotes. I will then place an order for 1BTC to buy/sell at the quoted price. I'm not currently looking at market depth. I have planned on looking at it later to figure out the max volume I could use any given time.
Also, yes, that was silly of me high volume = low volatility.

Can you be more precise about what quote your getting and what order you're placing? Are you trying to buy a particular offer you see in the market depth? (Also, higher volumes tend to mean less volatility.)

The problem might be that TradeHill adds orders to the Orderbook before processing them.
For example, this happened today:

Around 18h10 UTC, the highest bid was 4.842524 and the lowest ask was 4.840000
Around 22h00 UTC, the highest bid was 4.820000 and the lowest ask was 4.819900

I have also detected similar situations at ExchangeBitcoins.com.  CampBX  and MtGox seem to be matching orders before displaying them so you shouldn't have these problems there.
If you don't want to risk putting an order that will never go through, you should detect situations like this in your code and wait for the orders to solve. If the lowest ask is lower than the highest bid, something is not right.

Yes, i've just spotted that. I tried making an order for the quoted price and never went through even though I refreshed the ticker and the price was the same.
That's complete garbage, why do TradeHill do it that way?
Good tip on spotting the spread, i'll add that now. What kind of threshold should I have that could be considered safe for putting an order?

I noticed that you are using the ticker. I am talking about market depth so I am not sure how the ticker behaves in this situation... Anyway, I always wait until this is solved in the order book before placing an order. I have seen things like lowest_ask=12 / highest_bid=14 so I won't trust the numbers until they sort it out. Most APIs are very unpolished. I have found lots of other annoying tiny details.

Here's a post I made at bitcointalk regarding the issue.


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What are some good ways of marketing a Bitcoin related service to Bitcoin users?
What is a brief summary of some good ways of promoting a Bitcoin related service? This could include:

Bitcoin Service Directories
Forums
Advertising
Mailing Lists
???

The target audience is people who have bitcoin and know how to use it.
To avoid this question being too broad and requiring answers that are too long, I suggest keeping any summary of each item brief.

The folks at bitcoin.it run a moderated listing, https://en.bitcoin.it/wiki/Trade, which you can list at.  Another way is to work directly on reddit (r/bitcoin) and http://www.bitcointalk.org/.

There are few types of Bitcoin marketing off the top of my head

People who have Bitcoin and know how to use it.
People who heard of Bitcoin (in Forbes etc) and are afraid of it.
People who hear of Bitcoin (also in Forbes etc) and love it.
People who don't know Bitcoin but either { Like investment | gambling | Technology | financial theory }

Your question is too broad, so you will need to narrow down who your target audience.  Please revise your question, or else people on this site (potentially myself included) will vote to close the question as being "too broad".
(though I hope the closers give you time to read and update your question)

You can use all traditional SEO tools and services for targeted audience to improve your site in listings and accumulate traffic.
Additionally I could recommend using various micro tasks  such as blog posting and others to put as many links to your site on the web.

Post your website on Paid To Click websites dedicated to Bitcoin and select a good time for viewing your ads.
Example: On BitcoBoom (http://bitcoboom.com), you can start a campaign of 1000 users view for $1. Selecting 20-30 seconds to view your website will increase interest in your website ;)


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Can a bitcoin bank solve the problem of intensive value fluctuation caused by hoarding?
Let's assume a bank dealing in bitcoins is not any central of government bank that could control the money supply.
Instead, let's say there was a bank where the people would deposit money at some interest rate, and also the bank would give loans to the people at some interest rate.
The intention of the bank would be to keep the bitcoins in the circulation (by taking and giving benefits to the people with some interest rate) instead of hoarding, as we know hoarding may hurt the Bitcoin economy.
Or, suppose I deposit some BTC in HSBC bank (or some kind of reliable online bank), and HSBC will give the interest every month.

Related: http://bitcoin.stackexchange.com/q/408/516

I would compare 'Bitcoin' to 'Linux', when a traditional bank is 'Windows'. Even though Linux is great, finally, it is the effort of companies like 'google' and 'canonical' that's pushing adoption.
We certainly need some kind of bank that would simplify Bitcoin stuffs and make it more accessible to people; like, buildings bank like abstraction layer around Bitcoin (accounts, login, 2FA, etc.).
It would give confidence to people because they already learnt to trust such central authorities.
It would solve many problems and as already said in previous answer, 'hoarding' is not one of them.

Or, this Bitcoin bank could also just be a device, or smart phone, as well.

Unfortunately, it's not simple. The problem is that such a bank would be terribly vulnerable to fluctuating exchange rates.
For example, say the value of a Bitcoin doubled over three months. Suddenly, a large number of people who have loans will not be able to afford enough Bitcoins to pay them back. A large number of their loans would go bad all at once. Banks can't function if their loans are correlated in this way -- that's part of why a collapse in the housing market led to bank failures.
Basically, to make the risk tolerable, you'd need enough people willing to take short positions against the value of Bitcoins going up. It's not clear where those people would come from.

Saying people are hoarding bitcoins is out of focus: they are simply "not spending them" because there aren't enough ways to spend them.
Allowing loans wouldn't improve the situation, since there still wouldn't be many ways to spend those loaned bitcoins.
Finally, bitcoins already are a currency subject to deflation, and they are also (more or less) constantly gaining value against traditional currencies, so just holding them increases their value.
To sum it up, not a terribly good idea, and definitely not ground-breaking.


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How is hoarding to be prevented?
If all humans used bitcoins now (Jan 2013) for most of their transactions, then a dollar would be worth about a billionth of a bitcoin (1/10 Satoshi).
If bitcoins take ten years to catch on that fully, and population rises only a little while worldwide productivity doubles, then you could buy 5 candy bars for a Satoshi (1/10^8 BTC).
A house today, starter home might be worth 10 000 bitcoins or so. Paying a 30 year loan payment in Bitcoins would require a payment of a billion dollars a month at some point.
So I don't see how you could have viable loans in bitcoins until the system has settled down at least 30 years from now.
And if you have 1 bitcoin today, it could become worth 100 million dollars purchasing power in 10 to 20 years. One inexpensive coin worth an hour's labor.
So the system has an enormous potential reward for hoarding--far beyond working for a living, or any remotely normal successful investment.
How is hoarding to be prevented?
And I think this system is even more unsound than fiat money, albeit in a very different direction. But it IS likely to lead to drastically improved money in the long run.

For downvoters, I say this: the key question here is "How is hoarding to be prevented?", so I've edited the title to this. This is something that is probably on the minds of MANY bitcoin users, and is worth an answer. I'd like to see what feedback I get on my answer to this...

Actually my concern is not really that bitcoins would be hoarded--people have a right to save and to invest. Rather, that hugely disproportionate rewards harm the global economy. Early adopters are helping to solve the planet's current Dollars/Euros currency agonies. This is true even if bitcoin ultimately fails or is replaced by a similar alternative. Early adopters deserve a reward--but do they deserve the production power of a million people for a hundred years?

I upvoted you. Your question is very astute and valid. Unfortunately you were downvoted, because there are some unsophisticated thinkers here who have the typical goldbug delusion about gold and inflation.

possible duplicate of Does hoarding really hurt Bitcoin?

Why would you want to prevent hoarding? Hoarding is when a person gives something of value and gets nothing in return. That sounds like a pretty good deal for everyone else.

Key points in bold.
Hoarding doesn't need to be prevented. At least, not yet. See this answer for a solid argument: How does hoarding hurt Bitcoin?
Bitcoin attracts hoarding by design. To change that would turn it into something else.
As Bitcoin matures, I expect that it will remain a problem that speculative trading brings  instability to the market, similar to the gold market. If you put your retirement savings into gold, you'll likely do quite nicely, but there's also a significant chance you'll lose most of it in a price crash. It's not a reliable store of value. Even if you have several years you can wait for the value to come back up, you may still lose out.
Even though bitcoins are more efficient to trade than gold and cheaper to store, it's subject to the same volatility when traders manipulate it. The more popularity Bitcoin has, the bigger the traders will be that take an interest in it, like they do in gold. This could mean that when Bitcoin is mature we still see the same level of volatility that we see today with Bitcoin (and gold).
To me, this says that Bitcoin is great for efficient online transactions, but in the long run (once the market has reached its saturation point) won't a completely reliable store of value. For that, a diversified portfolio of productive investments is better.
If that becomes common knowledge, then people will eventually accept the volatility as a necessary risk in the use of Bitcoin. After all, on average it will still almost certainly cost less than credit card transactions and traditional international money transfers. Secondly, risk-reduction services (ie insurance) tend to fill gaps in the market like that for those who don't want to take the risk.
In the meantime, Bitcoin is doing a great job, but it doesn't mean something better won't come along.

You will do quite nicely in gold if you sell out before it peaks and declines again. Gold has never always gone up. And the gold cycle is very short, it was never a stable value for 1000 years. Please do some historical research to put some salve on your speculation blindness.

@ShelbyMooreIII, that's exactly my point! Did you read it too quickly? My comment says there's "a significant chance you'll lose most of it in a price crash"

Apologies you are correct. I tried to remove my downvote, but you would need to edit your answer first, then remind me to come back. Happy to see we agree on that aspect. Yet I don't agree with you that people will accept the volatility or that this is the best we can do with the design of a P2P currency. Specifically Bitcoin has nothing in its protocol to encourage the transactional value and discourage EXCESSIVE dormancy. Appreciation yes, but excess to ponzi yellow brick road no. My AnonyCash design is that balance.

@ShelbyMooreIII, updated. I think the volatility will need to be accepted by those that want to use it unless something better arrives on the scene. I agree with you that it's not a perfect solution, but it does beat credit cards in a number of uses, despite its limitations.

So let's try to make something better. If we fail, at least we tried. I believe in virtue. Like you probably do, I take pride in my work and try to create quality and help others prosper. I am not hiding behind anonymity.

Build in a reliable entropy function to take account of natural decrement in value over time. All value degrades in nature, and this is the fundamental problem with money in that it can be hoarded without cost.
Not sure how this would be implemented, it does dig at the root of the basic theory of money and value but that is what we are attempting to achieve so why not look at it.

IIRC, Timecoin has a feature like this.

I upvoted, bcz I am happy to see someone else understands that money IS NOT capital. Most people can't grasp that concept.

@ColinDean None of the links on that page seem to go anywhere. Do you have a link to its source code or binaries?

I don't, unfortunately. I think there was mention of it on /r/bitcoin.

I speak from the point of view as a middle-aged (Born 1968) investor; I think the answer to the question is quite simple. You cannot simply consider the start point and end point in asking the question. Along the way the price will gradually appreciate and most people have a price at which they will start to sell their Bitcoins. Currently I hold about 630 BTC. I acquired these over the past 18 months as I gradually poured about $6000 cash into the Bitcoin exchanges. At todays price I would get about $11000 if I sold them all.
August 2012, I took most of my BTC and invested in a BTC mining fund that pays around 5 BTC a month dividends. At todays exchange rates I could convert this to $85.00 a month. Currently I convert none of this back to fiat because my goal is to save for retirement, and I believe in BTC so I let it ride.  At some point in the future as Bitcoin becomes more valuable, one BTC will be worth say $1000.00. My 5 BTC a month dividends would yield $5000 a month. At that point (actually probably before) I will be using some of that to fund retirement expenses. I will sell that portion on an exchange (or better yet directly trade with a merchant) to provide the real world products etc. that I need to live on.
Of coarse those BTC would be worth even more in the future, but we all need to live and we all have limited lifespans, so at some point we will sell to provide for our needs. Actually this is true of any investment that will appreciate at a level above inflation. For example stock investments on average pay around 8% a year in the long run and inflation averages around 3% in the long run. If you have a diversified portfolio, no matter what it will be worth more in the long term future. All the time though investors are selling in order to fund their basic needs. This will be true of Bitcoin as well.
If people simply hoarded BTC then there would be none available on the exchanges. 6 Blocks are created each hour X 24 hours X 25 BTC per block yields 3600 BTC created per day. 30 days X 3600 yields about 108,000 BTC mined per month. The current 30 day volume on Mt Gox is over a million BTC (http://www.bitcoincharts.com/markets/mtgoxUSD.html), this would not be possible if people simply were hoarding them.
When one thinks about it, the actual value of BTC (or any currency) actually comes from the fact that people are willing to trade it for real world goods/services. Some people may hold larger amounts of BTC just like some people hold larger amounts of investments or cash in accounts. Hoarding will not be a problem as long as some people are willing to trade other items for BTC.

which market do you use for investing back into mining?

You sound like one of those speculators "until dust do us part". You will likely hold all the way to the bottom when Bitcoin's bubble is finally popped for good because "you believe". Religion and speculation are a powerful dustbowl engine. Your answer to his question is that some speculators cash out. Actually the truth is that all speculators end up destitute, even the greatest ones who were temporarily very wealthy. Because a gambler can never stop trying his luck. Do some historical and psychology research research.

@ShelbyMooreIII speculation and savings are fundamentally the same thing (as is hoarding for that matter). not all savers end up destitute - far from it.

So I don't see how you could have viable loans in bitcoins until the system has settled down at least 30 years from now.

Err.. For a home loan, that would be paid down after 25 years or so; I think you're underestimating. Let's look at the most popular non-governmental currency, gold. According to this, the price of gold (in US dollars) quintupled between 2001 and 2011. Keep in mind that gold has been used as a currency for thousands of years.

And if you have 1 bitcoin today, it could become worth 100 million dollars purchasing power in 10 to 20 years. One inexpensive coin worth an hour's labor.

It could also be worthless. Perhaps the various governments of the world will see Bitcoin as a threat to their ability to tax. The Bitcoin community can come up with a solution to any technical countermeasure, but that doesn't stop a crackdown against businesses that accept it.
It's not realistic to assume that everybody in the world will start using Bitcoin. It requires a computer/internet connection to even validate a transfer.

How is hoarding to be prevented?

People hoard their money because they believe it will be more valuable in the future. To stop that, you print money.

Yes, it is realistic to think everyone on Earth may adopt bitcoin. The worldwide web is creating a one-world culture and this level of communications means that people will want a common currency. The Euro and the US dollar are currently being ruined by excess printing and general lack of understanding of basic economics principles. The world seeks an alternative. Gold is reliable but you can't send actual gold over the web, so you're back to paper. bitcoin is a real alternative and may well succeed.

I wish I had enough rep power to downvote this. Nearly everything you wrote is factually unsupportable. 1) gold has not been used as a currency for 1000s of years. Most of the time it is not used and sits in vaults. 2) Bitcoin is not at all like gold for many reasons, and one major one is that the deceleration of debasement is over a decade or so, not millennia. 3) It is factually false that Bitcoin can technically adjust to any technical attack. If the attacker has a majority control of mining, upgrading the minority doesn't help— you must upgrade millions of owner's clients too. Chaos!


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Where can I see my Bitcoin address?
I use the original client, but I don't know where can I find my Bitcoin address. Can someone help me?

You don't have "an address", you have many addresses.  Though Bitcoin doesn't force you to do this, Bitcoin was built in a way so that you have a new address for each transaction where you receive bitcoins.

I think this question needs to be rephrased to include the version number, or it may become confusing as changes are made to the client. @Rowt, can you do that please, since you know which version you have?

Open the standard client
Go to "Receive coins" tab
You will have a list of addresses you can use

If you want to create a new address, just click "New Address..." on the bottom of the window.

IF you are running the MultiBit wallet, you can find your Bitcoin Address here:
1) Go to the Request tab,
2)

The is explicitly asking for the Satoshi Client, not Multibit.


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If I've lost my wallet, but know my bitcoin receiving address, can I get my bitcoins back?
Although I do have a backed up wallet file, I seem to also have a second bitcoin receiving address, which doesn't seem to correspond to it. Is there a way to recover any coins associated with that receiving address, or are the coins lost forever?

How did you lose your wallet? This might help us if #2 in my answer below applies.

How recent was that wallet backup.  Within the past 100 transactions (incoming / received) that you've had?

I had to refresh my computer do to updates and all my installed software such as bit coin wallet was gone after the process. I did back up my wallet almost everyday and also I did it on a external hard-drive,
but when I re-instal the bit coin wallet from bitcoin.org it give me a new receiving address and even if I have all back -up data and my previous receiving bit coin wallet where all my bit coins I have purchased were I do not know why is it not showing it in my new wallet. I have tried to recover and open my back up wallet files but it does not show my bit coins.
Please help. I did watch

You can't get your bitcoins with just the receiving address (if that could be done, they could easily be stolen), so your only chances of retrieving them are:

If they're stored in the wallet file you have backed up, then you can use that
Somehow recovering the original wallet file, which is a data recovery exercise. This might be possible in the case of a failure or deletion of a hard disk, or a deletion from an SD card/memory stick

It sounds like you have an old wallet backup that does not have the private key to the public address you are looking for. You are probably in the realm of data recovery.
I wrote a blog article that might help: http://gary-rowe.com/agilestack/2012/08/17/how-to-recover-your-bitcoins-from-a-failed-hard-drive/

And it should be made clear, ... if this was enough money to worry about -- STOP USING THE COMPUTER which had the wallet before it was lost/damaged/corrupted/etc. Chances of recovery may diminish each time your computer does anything to the hard drive.


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Are there any online wallets available for Litecoin?
Are there any litecoin wallets available on the internet right now? I have a mac and the mac version software is very confusing.

There are! Check the Litecoin Wiki for more information, and a list of services.

We have just released http://www.coinwallet.co which supports Litecoin.

Harborly is a US based litecoin wallet that also allows you to buy and sell with your bank account.

According to the current Wallet service overview of the Litecoin-Wiki there are six online wallet-services (copied from there):

liteaddress.org - Litecoin address generation tools
reddit ALTcointip bot - give and receive Litecoin tips from reddit users
Coinkite - Coinkite is a web wallet with merchant services, Point-of-Sale terminals and debit cards. Sign up here
CoinWallet.co - Online wallet
Harborly - Online wallet that can be linked with any US bank account
HolyTransaction - Online wallet, multi-currency support


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Are transaction fees required now? Is there any way to avoid them?
I have been using blockchain.info's my wallet to perform transactions, one of the reason I liked it was because I could choose to not pay a transaction fee. But recently I noticed blockchain.info's interface has changed, there's no way to not include a transaction fee now? (or am I wrong about that?).
Was there a change in the Bitcoin protocol to require transaction fee? or are there still clients available that has the function of not paying a transaction fee?

For the web-based hybrid EWallet or for the Blockchain for Android / iOS mobile app?

The web version of blockchain wallet.

Seriously they really got to stop demanding transaction fees. When bitcoin values go up, 0.0005 BTC will start to cost more and more. Imagine sending someone a $0.20 and being charged $0.30 for that...

Use Send Custom for full control over fees.
Click Send Money tab, then on the left menu under Transaction Type click Custom.
This URL might get you there.

https://blockchain.info/wallet/login#send-custom

I have tried it, but it seems even if I put 0.0 fee at that screen, when I review the transaction, a 0.0005 BTC fee is still included.

Use the Frugal option.  That way only the minimum (recommended) fee is included and only if the protocol rules require that you pay a fee.

What is the Frugal option? I'm trying to find out if there is any client that allow me to always avoid paying any fee, not even the "recommended fee". Are you saying the protocol now require a fee or else the transaction won't work?


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European online stores selling electronics
I know bitcoinstore.com is the heaven for bitcoin loving geeks to buy their gadget. However I'd like to find similar electronics stores in European Union area to avoid extra custom fees.
Are there any bitcoin-friendly stores in EU?

I've made several purchases from bitelectronics.net. As a bonus, Mikko, they're based in your (and my) country!

bitelectronics.net seems to have shut down.

Through websearch I have found e4btc.com. They seem to be based in Berlin.
I do not have any further experience or information about their offers, nor am I affiliated to them in any way.


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How to cash out E*Trade stocks (transfer funds from US to the EU) with Bitcoins?
My company has an employee stock purchase plan with etrade.com, but as I'm in Europe, I thought I could sell the stocks and save the bank transfer fees by using bitcoins.
You can sell the stocks online on NASDAQ though, but even to just place the order they ask for an bank account. So I either have to transfer to EU, paying the fee, or to an US account. As I don't have one, could I simply transfer directly to an Bitcoin exchange?

*You basically need to get money into E*Trades US back account.*
E*Trade will either want a wire transfer (from Europe) or a bank transfer from the US.
They have to be very careful about Anti Money Laundering. So  wont want to accept money directly from a Bit-Coin Exchange.
You can open a US account from your local EU bank. Your local bank will act as a proxy to make the required AML and KYC checks. You can then use bitcoin to route the money via a bitcoin exchanges to that account.
However if this is just a one off. You will probably find the costs, (fees at the EU exchange and the US one) and risk of bit-coin volatility; not worth the effort.
Remember this is a problem which existed before bitcoin. So there will be ways of getting it to work with out bitcoin.
I would contact E*trade EU and US and ask them what would be the best way to find you purchase. (E*trade EU may have an arrangement to do this simply, already)
If you are buying a large enough quantity of shares, then the wire fees etc will only amount to a few percent anyway.
That being said having a US acc would be useful for BTC stuff later on. For example if want to work remotely for a US company, and need an efficient way of transferring money regularly to you home currency personal bank account.

Oops sorry miss read your question (it is the other way around), either way it still kinda applies.

find someone that is interested in your stack, probably a bitcoin american tourist in europe, or someone that is in trading back and foward to europe


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Personal details disclosure when buying bitcoin
What personal information do you have to provide to buy bitcoins in the UK via a bank transfer?
I recently created a wallet on bitbargain.co.uk with the intention of buying my first bitcoins. I verified my phone number and entered my address details, however after this the website asked me to upload a photo of my passport or drivers license, a photo of me with my passport or drivers license, and a copy of a bank statement or utility bill with my address on it.
Is it usual for a website to ask for this information to buy bitcoins? Are there any other sites where you buy bitcoins via a UK bank transfer or credit card payment without having to disclose this information?

Policies will depend upon the exchange itself and setting up an account can take a good long while.
Some exchanges ask for less information, but I'd recommend being careful with using them. There have been some scams that have cost people large amounts of money.
Usually, exchanges want all of the information so they can increase security. As Bitcoins that are lost or stolen are nearly impossible to recover, exchanges want your personal contact information incase any legal problems come up. IE, you decide to run a scam yourself.
I'm pretty sure Mt. Gox has changed its policies. You now have to provide government issued ID to set up an account on Mt. Gox

All exchanges require detailed address and identity information.  In the U.K., the two exchanges are BitBargain and LocalBitcoins.  Both have the same policy.
My experience is that Bitcoin exchanges have the same or higher standards as do banks.

Yes that sounds a bit harsh, but it is not abnormal for exchanges  to request such information. Mt. Gox does this for example, but only if you want to increase you bitcoin flow through the exchange (i.e. a verified account or trusted account). According to the bitcoin wiki you can use Mt. Gox without any personal verification (except for an email address of course), but this imposes a monthly $1000 withdrawal limit and a monthly $10000 exchange limit. For most normal users this should be sufficient. Also be wary for any sites requesting a photocopy of your identification papers, as they could use it for identity theft. Make sure that you only upload such information to trusted parties!
PS. Please use some proper interpunction in your question, makes it a lot better to read!


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What is the most cost effective way to exchange USD for Litecoin?
Also, what risks are involved? Do the service(s) have a long track record?

You could try looking for someone to trade you USD for litecoins in your local area in person, through Bitcoin OTC Exchange, or perhaps BTC-E or some other online exchanges.
In the first case the risk should be fairly small, although it might take a long time to find someone, get in contact with them and so forth. Not to mention the exchange rate might not be in your favour.
The second option should give you better results, but you'd have to make sure you are dealing with someone reputable enough for your trade. However, finding an exchange rate in your favour might not be too easy.
Third option is probably the safest and the exchange rate should be reasonable. The main problem you might face with established exchanges is possibly having to register on them with your documents to avoid your account and funds being suspended due to Anti-Money Laundering laws and regulations.

Litecoinlocal is the best site for this, as you're exchanging your USD directly to a person for Litecoins via SEPA, ACH, or whatever payment method you decide on.

I recommend Litecoinlocal. However, from time to time I use http://bitbay.net.


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Does the U.S. Securities and Exchange Commission govern Bitcoin?
Do SEC regulations apply to:

Exchange of Bitcoin for US dollars
Investing in companies with Bitcoin
An exchange that sells shares of company stock for Bitcoin
Bitcoin futures contracts

Is a Bitcoin a security?   The SEC hasn't said that it believes it is and not communicated with or taken action, formal or informal, asserting that a miner is issuing securities or that exchanges are engaging as brokers of a security, which is a regulated activity.
Is a Bitcoin an asset or commodity?   Does your grocery store need SEC approval to sell bananas?   Or, more similarly, does a coin dealer need SEC approval to sell gold and silver bullion?
Now a broker where gold bullion is speculated on is regulated in the U.S., just not by the SEC.  The Commodity Futures Trading Commission (CFTC) is the regulatory body that addresses that.  To-date, there are no bitcoin-related services offering futures contracts, options, or anything similar which operate from the U.S.
Now issuing shares in a company is exactly the activity the SEC addresses.  There are no bitcoin-related services issuing company securities or operating a secondary market for shares that operates from within the U.S.  The regulators may still assert jurisdiction though if securities are offered to investors from the U.S.
Now there may be registration requirements for an organization that holds deposits or where an exchange interacts with the banking system they may need to register as a money transmitter, but that is not something under the SEC's purview.


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Upper and lower bounds of the amount of bitcoins?
As far as I understand, the bitcoin has an upper limit of 21 Million possible coins. Thus, the price of 1 coin, can in theory climb and climb. However, on the other hand, it seems like the system can handle 10^(-8) of a bitcoin.

Is this observation correct?
Is it already possible to have transactions of fractions of bitcoins?
If (1) is true, how can this fact influence the bitcoin's rate? In some sense, it means that the limit on the number of units is somehow much higher then 21M. Or more generally, how should its rate be interpreted given the existence of such tiny fraction of the unit?

Yes, there are 21 million whole bitcoins, each divisible up to 10^-8.
Yes, transactions for fractions of bitcoins are quite common, just as transactions for fractions of dollars are common.  I could send you 0.00000001 BTC if I were so inclined.
I can give you 1 dollar or 100 pennies, but the existence of pennies doesn't really influence the exchange rate of the dollar.

While the existence of pennies does not affect the value of the dollar, I do not think that is the question OP was asking. The fact is that since total BTC is fixed at 21M, the value of a satoshi goes up when that limit is reached. As the number of BTC in circulation can only go down past 21M, bitcoin are intentionally deflationary.

Correct, but coins have been lost, so although up to 21 million will be mined, there will be fewer than that in circulation.
Seeing fractions is routine, but sending and receiving bitcoins with a smaller fractions  will incur a processing fee.
#1 is true: The finite amount of bitcoins is actually expected to produce bitcoin deflation in the future, so its value will go up (constant supply and assuming increasing demand). However, the protocol can be adjusted to slice bitcoins even smaller then the current 8 decimal places. It's uncertain economic territory.

The Bitcoin protocol allows for 2,099,999,999,999,999 satoshis to be issued.
1.0 BTC = 100,000,000 Satoshis.
With about 7 billion people on the planet, that means the 2,099,999,999,999,999 satoshis divided among the populations leaves 300,000 satoshis per person.
If the value rises such that even a since satoshi rises significantly (e.g., above a penny) then further divisibility is an option.
But further divisibility is not something that impacts the value.  A dollar doesn't buy more after you first convert it to 100 pennies.  You still have a dollar's worth of funds.