Ok... this is a really unusual way to find beta on my account...
Was leveling an alt character in game when I swear I saw an email from blizzard pop up on msn but when I went to my inbox there was nothing. Since I was there I decided to check my mail and junk mail. In my junk mail I found something from WoWAccountReview@eu.blizzard.com which im pretty sure was not the thing I saw. I wondered if it was a scam or legit, since it was from eu.blizzard.com and I am not from eu.
So since I was logged in, rather than logging out and trying to log back in, I opened up my account management page that I have bookmarked/favorited (so I know 100% its safe) and tried to log into my account to find it saying the password was invalid. I have an authenticator so its not like someone else should be able to access it. I did the password recovery/change and logged in just fine to see cataclysm beta on my game list.
I have not recieved an email from blizz saying I'm accepted to beta, which I know is supposed to be later than when it's on your account, but I wonder if blizz somehow reset my password when they added the beta to it and thats why it wouldn't let me log in until I changed it again.
Run a virus scan and everything on your computer. You could have a key logger.
when you go to log in, it will say something like "authenticator number wrong" but in the background its being sent to some chinese kid who has a few seconds to do whatever to your account.
Just a coincidence really. I got a beta invite and I never got a real email from blizz. As for the password thing... do some virus scans, but I'm thinking you just mistyped your pass.
Blizz did say that beta invite wouldn't be going out by email and the best way to check for it is on your account management page, since its activated for you.