[throw_away_777]

There are ways to detect cheating on chess websites, though these methods are not perfect. The two main signatures are:

1) Playing moves that the engine recommends consistently. This looks for people who are inhumanly good, even the top chess players in the world regularly deviate from engine suggestions.

2) Time between moves always takes a minimum threshold, the time needed to relay the position to the engine. Humans vary wildly in the time thought based on the position, in a way that cheaters do not.

Neither of these detection methods are perfect, especially for small numbers of games. I don't think we will see large prizes for on-line chess tournaments because of possible cheating.