I wouldnt worry too much about cheating in MTTs. For one they have to be at the same table, which is unlikely. Secondly, even if they are at the same table, all they can really do is softplay, share their 2 cards with each other and try to collude to make people fold or put more money in the pot.
It's fairly obvious when people collude to whipsaw/make people fold, and they are easily caught. I've caught people doing it in ring games and after the 2nd time it was totally obvious what they were doing. Emailed suport and they got banned for good.
In sit n goes, especially the double or nothing/double ups it is a much more lucrative undertaking and a serious problem. Softplaying in such a flat structure like that gives a great edge to the others involved. This is where the chinese cheaters were found, and I believe they've been dealt with already, or PS support is in the process of dealing with them.