Blizzard shut down the Diablo 3 auction house after a gold-duping bug was discovered, but not before unscrupulous sorts generated obscene amounts of funny money. When auctions re-opened over the weekend, Blizzard was already auditing accounts to track down duped gold and punish exploiters.
Some players called for a full rollback on the servers to stop duping gold from wrecking the game's economy, but Blizzard was confident it could catch cheats.
"The vast majority of players did not participate in the exploit and we didn't like the idea of punishing them for the bad behavior of a few people," production director John Hight explained in a forum post on Friday night after the auction house returned. "Many players made significant accomplishments in the game that required time and dedication, and we felt it was worth the work involved to try to preserve these efforts and go after the exploiters instead."
In short, an overflow bug in the real-money auction house meant that people selling large amounts of gold for cash could cancel the auction to receive back more gold than they had put in. Rinse and repeat until you're sitting atop a shifting mound of dodgy gold. We know what happens when people can pull tricks to make magic money, right banks, yeah, right? Political humor, innit.
"Only a relatively small number of players had the billions of gold necessary to exploit the bug, and only 415 of those players chose to use this exploit for personal gain." Hight said that as of that post, Blizzard had already "recaptured more than 85% of the excess gold from the accounts involved."
Blizzard plans to donate proceeds from the cheats' auctions, as well as its own transaction fee, to the charity Children's Miracle Network Hospitals. It's also punished people who aided cheats by holding onto items or gold.