Sure the email wasn't a phishing attempt?.. Or your password no longer works?
My World of Warcraft account got hacked in 2010, by brute force. The cleaned out our guild vault, with our guild having over a hundred active members. Ouch.
Despite Exalted guild status, I got booted, and haven't been in a guild since. Part of me is happy that they had a very difficult time replacing my ultra geared Holy specced Priest, as the guild's primary raid healer.