I do want to put forth this to the above.
Blizzard is aware of the events that have happened with accounts- being hacked.
They have had this issue stemming from WoW
those who have that game along with Diablo 3 seem more likely to have been hacked.
Or anyone who got a trial from a friend from WoW likely were hacked,
Or even further those who played the beta, with a battlekey.
Those who did not do any of the above. No Arms you didnt correct?
I know its another means but an Authenticator has been effective, and free since WoW had so many issues.
Its not even a headache to setup.
Also anything you have lost with the exception of gold can be retrieved, as long as you have the full game- Call Blizzard. they are used to this and are very quick with the fixes.
I have two friends who had it happen after they got a beta free pass- and then bought the game- i never had the free pass, Blizzard retrieved everything they only lost 4k gold