If you’re concerned about cheating in poker, especially online, the only realistic type of cheating that does go on is collusion. It’s not as common as it was before, but on a rare occasion I still run across some idiots that think they can get ahead by playing together and sharing info.

It’s done by two or more players all playing at the same table and communicating with each other via telephone or something like MSN. They know each other’s hands and try and force players out of hands by raising and re-raising each other, then one of them folds on the river once they’re head to head.

Unnoticed it can make a small amount of profit in the correct setting. It doesn’t take long to recognize when you’re in a situation where this is going on, and most sites can recognize this behavior once it’s pointed out to them through hand histories.