Infection

Infection is a multiplayer gametype in Halo 3, discovered by beta source code hackers. It is the "official" Zombie mode after it's popularity as a custom game mode in Halo 2. The object of the game is for the "human" team to stay alive as long as possible using a starting Shotgun and/or various weapons around the particular map; however, the goal for the "zombie" team is to kill, or "infect" the "human" team using only Energy Swords. The game is played in rounds with no apparent "teams", except for the in-game notification of which team you stand with.

It should be noted that during Infection, a zombie's abilities to pick up additional armament has been disabled.