What is a spirit attachment? This is a multi-part question.


what is a Spirit Attachment?  


For those that believe in it:


what is it, 
how does it work, 
how does one protect ones self from it?
Spirit attachments would be spirits that attach themselves to a human life.  This was evidently more common or at least more identifiable during Jesus incarnation as reflected in the following gospel accounts:


  Matthew 8:16 When evening had come, they brought to Him many who were demon-possessed. And He cast out the spirits with a word, and healed all who were sick
  
  Matthew 10:1 And when He had called His twelve disciples to Him, He gave them power over unclean spirits, to cast them out, and to heal all kinds of sickness and all kinds of disease.
  
  Mark 3:11 And the unclean spirits, whenever they saw Him, fell down before Him and cried out, saying, “You are the Son of God.”


The following scripture provides insight into so called “spirit attachment” and how they work.


  Matthew 12:43-45  “When an unclean spirit goes out of a man, he goes through dry places, seeking rest, and finds none. “Then he says, ‘I will return to my house from which I came.’ And when he comes, he finds it empty, swept, and put in order. “Then he goes and takes with him seven other spirits more wicked than himself, and they enter and dwell there; and the last state of that man is worse than the first. So shall it also be with this wicked generation.”
  
  Mark 5:13 And at once Jesus gave them permission. Then the unclean spirits went out and entered the swine (there were about two thousand); and the herd ran violently down the steep place into the sea, and drowned in the sea.
  
  Luke 8:2 and certain women who had been healed of evil spirits and infirmities—Mary called Magdalene, out of whom had come seven demons


Notice these spirits seek residence or a host; evidently their wills can be exerted upon God’s creation more easily through a host.  Hosts are anything from Mary Magdalene to swine.

Biblical behavioral modification comes through authority; Christ has supreme authority within this realm and His authority can be extended to His disciples. 
Predominantly spirit manifestations are identifiable through the host’s behavior, but there are indications within the above verses that physical infirmities can also exist.

Since the abolition of superstition few attempt to reconcile the influence or even the viability of spiritual influences within our daily life.  Certainly Paul was not unaware of spiritual activity as proven in his Ephesians 6:11-13 warning:


  Put on the whole armor of God, that you may be able to stand against the wiles of the devil. For we do not wrestle against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this age, against spiritual hosts of wickedness in the heavenly places. Therefore take up the whole armor of God, that you may be able to withstand in the evil day, and having done all, to stand.


Today, Christians have to negotiate between “realities”.  Christians believe in a “spirit” reality and that the “spirit reality” impacts our daily lives.  To deny this is to deny that the Holy Spirit is real and capable of influencing our daily lives toward God’s will.  Modern Christians also have the benefit of understanding neurological and circumstantial behavioral influences as well.  Faith, hope, peace and joy are real human encounters that generally cannot be dismissed through empirical observation.  Love of course is the most difficult reality to understand merely from this physical perspective. 
The whole armor of God consists of: the shield of faith, which is always employed in the love of God.  When we trust God’s love the enemy of God stands condemned, for that is exactly what He failed to do.  We are to put on the helmet of salvation and carry the sword of the Spirit, which is Christ, made manifest.  This is revealed in the early verses of John, “in the beginning was the Word and the Word was God…all things that have been created were created by Him…and the World became flesh and dwelt amongst us…
The waist must be girded by “truth” upon which the breastplate of righteousness rests.  Our feet should be prepared to bring the gospel of peace.

Finally in Ephesians 6:1 


  praying always with all prayer and supplication in the Spirit, being watchful to this end with all perseverance and supplication for all the saints