Players have discovered (and exploited) a dupe bug in World of Warcraft. This is the worst kind of problem to have in any multiplayer game. A few abusers can destroy the economy of a game in hours (literally) by adding huge amounts of illicit cash into the economy. Interestingly, the gaming community seems eager to blame Chinese farmers for the problem, but I think it was almost certainly American ingenuity.
Blizzard hasn’t announced how they’re going to resolve the problem yet, but given the scope it seems like it’s going to be painful for them and the player base. (I wouldn’t be surprised if they have to roll the servers back a week or so, which would be really painful.)