According to EuroGamer.net Diablo 3 accounts are already being hacked and their accounts stripped bare. I’ve not bought D3 yet, but if accounts are already being hacked, BEFORE the Real Money Auction House (RMAH) goes live, this doesn’t bode well for the typical gamers once the RMAH goes live and real money can be stolen. My advice, either just wait and buy Torchlight 2, or if you really wanna play Diablo 3 get yourself a Blizzard authenticator. You can get a physical authenticator direct from Blizzard here or if you prefer look around the same website for how to get a smart phone app to do the authentication for you. Battle.net is know to be hackable so protect yourself and your game.
Consider this a PSA.