Just for fun and curiosity: is there cheating on professional chess tournaments/games? Just for fun and curiosity. Has any GM ever tried to cheat during a game? Maybe even making (on purpose or not) an illegal move that was not caught by his opponent?

NOTE: Of course when you are playing on the computer there is no cheating, because the computer won't allow it. I am talking about face-to-face real-life games.
There have been cheating scandals in top level chess, most notably in 2010 involving French top 100 player Sebastien Feller and in 2012 involving German GM Falko Bindrich.

These two scandals involved computer assistance. There are other forms of cheating, like throwing games, which are harder to prove. 

Illegal moves aren't an issue, but Kasparov allegedly violated the touch-move rule in a game against Judith Polgar.