Reports are coming into Eurogamer from multiple sources that Diablo III accounts are being compromised. Once compromised, items and gold are being removed. Even Eurogamer writer Christian Donlan found his account victim to the hackers. Control was handed over to "Anna" as the picture below shows.
Blizzard is working quickly to resolve player complaints by rolling accounts back so that they get all of their items back. Unfortunately, during this process, players can lose levels and progress. It's an unfortunate side-effect, but probably not as bad as the loss of the items. These hacking reports coincide with reports of the EU Diablo 3 servers going offline Sunday.
On Sunday, the servers were down for about 4 hours. Some are speculating that the servers were taken offline due to an SQL injection attack, but these speculations are completely unconfirmed. Blizzard offers an account Authenticator, but it seems as though people who were using it were also victims of the hacks. Blizzard will need to resolve this before they can release the real-money auction houses. Blizzard has yet to respond to these reports.