This account has been found to have employed third party software designed to automate many aspects of the World of Warcraft game play experience. Such software runs contrary to the essence of World of Warcraft and provides an advantage over other players. In addition, use of this software can lead to exploitation and destabilization of the World of Warcraft server economy. As such, this account has been closed and will not be reopened under any circumstances.
While ominous, it sounds to be a case of a problem with Blizzard's automated anti-hacking scans. TransGaming (makers of Cedega) is currently working with Blizzard's engineering team to resolve the issue -- and has been told that it wasn't Blizzard's intention to ban Cedega players. If you're a Cedega player who has suddenly been banned, Transgaming is offering to help reinstate your account -- let them know you've been banned and give them your account name, either via this support thread or e-mail to their support team.
[Thanks to Pat and Druid dude. Cedega links via Slashdot.]