A Halo modding community has accidentally made various hidden game files public, found by retrieving hidden data in the Halo 3 Beta code. They reveal new weapons, vehicles and equipment and also suggest new modes and rankings for the full single and multiplayer game.
Before we go any further, a warning: the following are in no way official or confirmed features of Halo 3, but they do appear in the Halo 3 Beta code in some form too complicated for us to comprehend or explain. We're just the messenger.
Smoke (suggested this might be a smoke grenade?)
Infection (described as "Destroy the Flood or become infected. Score points for killing flood or big points for infecting a human. The player with the most points wins."
The highest rankings are now Killpocalypse and Killionaire, instead of Double Kill and Triple Kill.
A reference to a map editor has also been found, a returning feature from Halo 2.
The information has since been removed from the forum in question.