I recently got a mail from Blizzard that my WoW account had been suspended for gold farming. Since I hadn't been logged in for 5 years or so (I have no idea), I decided to see what they were on about. It turned out some Chinaman had cracked my password and created lots and lots of level 1 characters on my account! It was funny. I changed the password and didn't think more about it.
Now I get "someone has requested your password to be changed, click this link to change it" mails every day. I guess Chinaman is eager to get back to his farming..
Similar happened to me, authenticator cured the problem.