Hacked account, how did they do it?

[Korruptor]

I have my 5 accounts across 5 separate battle.net accounts. The same authenticator can be linked to all 5, and then I can broadcast the same single code to all 5 when logging in.

The only reason I wouldn't do it this way myself is that if you don't log in with all your accounts every time you type in your authenticator code you leave the idle account(s) open to attack.