The video above claims to demonstrate a new exploit found in Diablo III that, get this, allows players to become invincible. That is not an understatement: the video's narrator shows his character simply not taking any damage, plowing through enemies with next to no effort.
The loophole only seems to work for Wizard class and renders certain effects unusable. That being said, it apparently works for any difficulty, and makes you, well, unbeatable.
The official Diablo forums are abuzz with people confirming the exploit works and even sharing steps to reproduce it. On the other hand, no one from Blizzard has made mention of the bug and as this post is being written, it is still confirmed active by Diablo III players.
If anything, Blizzard will no doubt be examining and presumably fixing this issue as soon as possible, if for no other reason than the effect a bunch of invincible players with items to sell will have on the Real Money Auction House.