It's a game about zombies.
A very simple game, in fact. Point on the screen near a group of people, and those nearby will become zombies (most of the time). Helpful hint: try to infect stronger enemies like police, soldiers, gangsters, terrorists, or Eskimos.
Upgrade them to make them stronger, faster, and more infectious. Also included are "special" zombies like undead Ronald McDonald and Colonel Sanders.
Starting in Africa, Spread your Infection across the globe to places like Tokyo, New York( where you can attempt to Infect Spider-Man), and the North Poll (where you can unlock Zombie Santa).