According to Dawn of the Dead, when hell is full the dead will walk the Earth. If that's the case, then the digital version of hell must be stuffed, because zombies are showing up more and more often in gaming. In fact, two of the season's biggest games have zombies in them. Left 4 Dead from Valve pits you and three other players against a modern-day zombie apocalypse. The other isn't a game that you expect to be included here, but Call of Duty: World at War from Activision and Treyarch features a bonus level that has you and three others hold out against waves of Nazi zombies.
Both games have co-op action with up to four players against the undead, so it's tempting to draw comparisons. So IGN did.