Update 2

The War Z has been removed from Steam's new release list. Valve has provided a statement regarding what's going on:

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"From time to time a mistake can be made and one was made by prematurely issuing a copy of War Z for sale via Steam. We apologize for this and have temporary removed the sale offering of the title until we have time to work with the developer and have confidence in a new build. Those who purchased the game and wish to continue playing it via Steam may do so. Those who purchased the title via Steam and are unhappy with what they received may seek a refund by creating a ticket at our support site here ."As of now, The War Z is still listed on Steam , but it can no longer be purchased. Since the "Foundation Release" of The War Z on December 17 it was the top selling game on Steam.: Following the release of The War Z it became clear that several of the features listed on the Steam page description were not actually in the game. The listing has since been amended. GameSpy talked to Hammerpoint Interactive to find out what happened and received some very interesting answers : Hammerpoint Interactive's game of survival and zombie slaying, The War Z, was released on Steam today. This launch of the "Foundation Release" version follows periods of beta and alpha testing that ran earlier year.In the game you spawn into an online open world and must find supplies to survive while dealing with bloodthirsty zombies and other greedy players who want to take your stuff. According to Hammerpoint, The War Z has so far had 600,000 player registrations and is played every day by over 150,000 people.On Steam The War Z costs $15 , though you can also pay more if you're interested in bundles of virtual currency. Hammerpoint has promised to continue updating the game after this launch, but did not specify which features and content it would focus on delivering next.You'll find more War Z coverage soon and eventually a review on IGN.