The War Z didn't go down very well when it was released. First there was uproar when the game was mis-advertised on Steam, forcing Valve to pull the title from its listings. Then when players logged in and discovered that the game wasn't very good (it's got a current Metacritic rating of 20 if that's any indication), and that it was rife with spawn-killers and hackers, it became even more notorious.
The much maligned survival horror MMO has now been rebranded, and its new title is Infestation: Survivor Stories. OP Productions declared it to be because of a trademark issue (Day Z possibly, or maybe even the recent movie World War Z - neither of which would appreciate the association) in a recent post:
Effective today, The War Z has changed its name to Infestation: Survivor Stories. This change has come about primarily as a result of some confusion and trademark issues with a similarly titled property. While we were reluctant to rename the game so long after launch, especially with nearly 1 million registered players, it was ultimately decided to be in the best interest of our existing community as well as future players in order to eliminate confusion. Please rest assured that this will in NO WAY affect you as players. The only difference you will see is the change in logo and website. There will be no interruption of service or change in content.