Very recently, a hacker (Jadd?) or a group of hackers (Jadd, Master674, and Cencil?) most likely from OwnedCore (formerly known as MMOwned) discovered an exploit that would allow them to either activate GM spells or custom spells, that would kill anyone in range instantly.

If you dig around the forums, you may find someone else had a past in having fun with the WoW game there as well  But that was a looong time ago. 


References:
http://wow.joystiq.com/2012/10/07/reports-entire-cities-dead-on-certain-realms/#continued
http://www.ownedcore.com/forums/world-of-warcraft/world-of-warcraft-general/380545-hackers-orgrimmar-twisting-nether-eu.html
http://www.ownedcore.com/forums/world-of-warcraft/world-of-warcraft-exploits/380575-breaking-exploit-news.html