In a US forum thread, players have reportedly already lost hundreds of thousands of gold. Further, many of these players have Blizzard Authenticators attached to their accounts. Similar reports are coming in from the EU.
There is reported confirmation from GMs, alleging that the technical team are aware of an issue, and advising the player in question to add SMS Protect to their account to safeguard against any potential further issues. If you would like further information on adding SMS Protect to your account there are video guides available. Of course, it is also important to maintain an authenticator on your account, as well as running regular virus scans, malware scans, and keylogger scans, as well as using unique passwords for your battle.net account.
We have reached out to various contacts at Blizzard Entertainment for comment. We will provide any updates to this developing story here.
Update 12:50pm EDT: We're getting reports that the Auction House on some realms have been closed. The Mobile Armory Auction House also appears to have been closed, confirmed by Blizzard EU via Twitter:
The Mobile Auction House is currently down for maintenance. We don't have an ETA yet, but will keep you updated.- Blizzard CS EU (@BlizzardCSEU_EN) June 22, 2013