The massacre apparently resulted from a previously unseen exploit that let level one characters access the kill commands for every player and computer-controlled character in the area. A few quick-witted players managed to record video of the massacre as it was happening, showing characters dropping left and right in the formerly safe confines of the cities.

Blizzard quickly issued a hotfix for the exploit, which it says “should not be repeatable.” The company is now conducting a “thorough investigation” into what it considers a very serious matter. “We apologize for the inconvenience some of you experienced as a result of this and appreciate your understanding,” community manager Nethaera wrote in an official forum post.

via Hack temporarily turns WoW towns into piles of corpses | Ars Technica.

Also, old news; virtual viruses. not exactly computer viruses.