Probably due to your iPad/iPhone trying to log in over and over with an incorrect password. That's what did it for me, no hacking, no password phishing, just my iPad locking me out of my account.
Bloody stupid policy. I'm happy with my WP7 phone though. I have money set aside for a new phone still. Every time i think of getting a 4S i remember this and i put my credit card away.
EDIT: i can't believe i was voted down on my earlier posts because of bad customer service i received.
And today my better half has been told her account is locked and needs to change password. Interesting how these 'hackers' always hack just after an iOS update.