Some particular user going by the name ‘Jadd’ has posted a video claiming to have nuked entire cities. There is no official news of Blizzard as yet about the reason behind the dead cities. We have got the videos [below].
[Update]: There is a lot of chatter on Ycombinator and WOWInsider about this story.
via Entire Cities in World of Warcraft Dead, Hack Suspected – ParityNews.com: …Because Technology Matters.