Diablo 3 was briefly rocked by news of an exploit that allowed players to do this, click here, and boom, invulnerable Wizard. Normally, something like that would be a cute bug, but Blizzard has a real money auction house to protect. So Blizz patched it, maybe. While they were looking at the Wizard, though, the Barbarian busted out his own invulnerability exploit. The trick is to use a certain power right before a cutscene, leaving the game to think that power is active all the time, forever after. The Verge has the story.