Going Loud Studios have developed Zombian accountant. The story line is that a terrifying zombie outbreak threatens to consume humanity and you are his victim to the undead curse, doomed to hunger for human flesh. In a startling turn of events, the army actually manages to contain and eliminate the threat. In most zombie games, players get extra points for hurting humans but not in this game. This WP7 game costs 1.29 dollars and there is a trial version as well.
Also, make sure to check out Zombidemix which is also a Zombie Game