Blizzard appears to finally be getting Diablo III’s rocky launch problems under control. In a lengthy post to the Diablo III forums, Blizzard assured players that the number of recent reports about compromised accounts were small in number and mostly the compromised accounts were accessed by traditional means.  

Blizzard also addressed the reported “session spoofing” method that some players claimed was being used to access certain accounts.

To that end, we've also seen discussions regarding the possibility of account compromises occurring in ways that didn’t involve these "traditional" methods -- for example, by "session spoofing" a player’s identity after he or she joins a public game. Regarding this specific example, we've looked into the issue and found no evidence to indicate compromises are occurring in this fashion, and we've determined the methods being suggested to do so are technically impossible. However, you have our assurance that we’ll continue to investigate reports such as these and keep you informed of important updates.

Diablo III has a number of hotfixes in the works and a game update planned with next week’s downtime to address client issues and several bugs. Additionally, the real-money auction house that was originally scheduled to release a week after the official launch of Diablo III, and was previously pushed back to May 22nd, has now been delayed once again. No new launch date has been assigned for the feature as of yet.

Source: Diablo III Post-Launch Update