Of course, rumors abound as to just exactly what happened. Most people point towards it being a hack, and there's some videos out there floating around that give credence to this theory. Has it happened on your realm? What on earth is going on? And what do you think is causing it?
Update: Blizzard has posted on the forums, informing us that this exploit has now been hotfixed.
More screenshots as they come in after the break.