Authenticator Suddenly Attached to Account

I have not been active on this account since wotlk was released, having played on the european servers. I moved to the US recently for studies and have had my account active for approximately two weeks now. This morning I could still log on, but this afternoon an authenticator window suddenly popped up. I did not link my account to an authenticator.

As a result I am unable to log into the game or my battle.net account, but I have been able to change my battle.net password. I also changed the password of my email address. The virus/spyware scan didn't find anything, and it appears as though my characters are still dressed on the armory.

I live in a dorm, but none of my roommates play WoW, or know my password. I access the internet wirelessly through a router one of my roommates brought. Since I am not a tech genius... could that compromise my computer in some way? And if so, how can I up my security (aside from keeping the computer updated)? I use a Mac.

I've submitted a web form, should I call billing as well?

Any assistance will be greatly appreciated, thanks.

P.S. For curiosity's sake, can someone explain to me how I am magically logged onto the forums (without having to type any login info) if the authenticator prevents me from accessing everything else?