While chip dumping is probably more common i think it is most likely more effective of mathematically knowledgeable poker player to be on the phone sharing whole cards. Then they can often have u drawing to less outs than u think and although appear to be giving u good pot odds
actually be giving you slightly worse odds. This makes it much more profitable for a cheat to simply share whole cards.
If u like multi table tourneys you are probably much less likely to encounter cheating as the players cheating will need to be at the same table. SNGs and cash games are much more likely to have cheaters for the obvious reason that u can choose your table. Don't forget that u can always stand up from a cash game when you suspect someone cheating.