Cheating.....

[HopeydaFish]

The only "real" cheating you have to worry about is people colluding at the tables. However, it's usually pretty obvious (to an observant player) when your opponents are colluding, and you can quickly report the colluders to site's security if you are at all suspicious. Once the site views the players' hand histories, it is obvious whether or not the players are in cahoots. They'll even share the results the investigation with you, in order to try to assuage your fears.

Sites have an immense amount to lose by allowing cheaters to prosper. They want to stamp out cheating even more than the players do.