Zombies

Were you looking for the Flood, a zombie-like species inhabiting the Halos or Infection, a multiplayer gametype in Halo 3 and Halo: Reach? Zombie (or Zombies, Pandemic, and Dawn of The Dead) is a fan-made gametype originating in Halo 2. The popularity of the gametype prompted Bungie to officialise the gametype in Halo 3 as Infection.

Overview
The basic rules of Zombie involve two teams: a small starting green (or blue in some cases) team and a relatively large red team. There are no shields; red sports shotguns and magnums and green (the zombies) sports energy swords.

Whenever a red team member is killed, they must switch to green team. The ultimate goal is to last as long as possible without getting killed by the Zombies, and becoming one themselves.

Infaction gametype
The Infection gametype was created by Bungie for Halo 3 following the popularity of Zombie in Halo 2. The gametype features the living death known as "Zombies", with quotes such as "Infected" and "New Zombie" commonly appearing. The aim is for the Zombies to kill all of the living to join their ranks.

Trivia
Initially, the game variant has honor rules, meaning there is no in-game mechanic that forces the a red player to switch teams after being killed (infected). Halo 3 's Infection Mode, however, forces humans to become zombies after being killed, eliminating the honor rules.