Infection

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Infection is a multiplayer gametype in Halo 3, Halo: Reach, and Halo 2 Anniversary. It is the official Zombie mode, modelled after zombie mode's popularity as a custom game in Halo 2. In Halo 4, the gametype was tweaked and permanently renamed Flood.

Description
The object of the gametype is for the players to stay "uninfected" as long as possible while the zombies try to kill every living player. The number of players starting out as Zombies, "Alpha Zombies", can be changed in the options and are selected at random from the start. When a Zombie kills a "living" player, they are "infected" and they become a zombie. When there is just one living player left, he/she is declared "Last Man Standing".

Medals

 * Zombie Killing Spree - Kill five zombies without dying.
 * Hell's Janitor - Kill ten zombies without dying.
 * Hell's Jerome - Kill fifteen zombies without dying. (Not in Halo 3)
 * Infection Spree - Infect five humans without dying.
 * Mmmm Brains - Infect ten humans without dying.
 * Thriller - Infect fifteen humans without dying. (Not in Halo 3)
 * Last Man Standing - Be the last human left alive in the round.

Halloween
On October 31, 2007, a specialized Halloween Matchmaking playlist was available, which played this game mode with up to 13 players (it being an "unlucky" number). This game type's popularity allowed it to become a "regular" among Double EXP Weekend games. It was repeated again on October 31 2008, but unlike other occasions, the October 31 2007, 2008, and 2009 ones were Ranked. The others were mainly Social.

Double EXP Weekend
On April 10th, 2008, the playlist came back for a Double EXP Weekend as Living Dead, also starting with exactly 13 players. Living Dead also appeared on the weekend of May 22 and on the 28th August. Living Dead is a Double EXP Weekend game with many games. Infection games have also appeared in other Double EXP playlists such as Turkey Day, the 2008 Thanksgiving weekend playlist.

Halo: Reach
In Halo: Reach there are two default variants: Infection and Safe Havens. By default zombies have the Evade armor ability, move faster, and can jump moderately higher than humans, making them harder to kill. In Safe Havens humans can only deal half the normal damage but can still kill zombies with a head shot. Safe havens grant only humans inside it invincibility and normal damage until they leave its boundries or it moves. The effects the havens give can be completely customized as well as the rest of the variant. It should be noted, however, that if an infected player quits the game then a non-infected player will take his/her place. It's unknown if this is a bug or if it was intended. Either way, this can lead to confusion to the switched player. In May 2011, Bungie released a new Infection gametype called Alpha Zombies. In this version, the players who start off as zombies have a red armour colour and have unlimited sprint. Also, the zombies have little health (4 pistol shots to kill). The lobby size was increased to 12 people. Safe Havens seems to have been removed from Matchmaking as well, along with certain maps such as Pinnacle to ensure that the game was fun for both teams. Some exploitable areas have also become soft kill zones to prevent survivors from sniping zombies with ease.

Tactics and Tips

 * If you are making an Infection game, try to make it very balanced. For example, give the zombies 200% health but no shields and only slightly higher speed and jump. In turn, give humans Shotguns and Pistols with limited ammo. Also, when making Forge maps, if you make a hiding room for survivors don't make it impossible for zombies to get in. Instead, give the room two entrances the survivors must work together to guard. Another fun thing to do is to put breakable or movable items such as barrels and palettes in front of doors to barricade them.
 * By default, regular zombies use Energy Swords, hence has limited/short attack range, and cannot pick up weapons. As such, it is recommended for the player to be equipped with a ranged weapon such as the Battle Rifle or the Covenant Carbine.
 * If you are playing as a zombie, its a good idea to put on Active Camo, so you can sneak up unnoticed or stalk the humans from behind, making sure they don't see you.
 * Yet another tactic that the "living" use is called "baiting". The players gather in a small, confined space; preferably one with only one opening. Whenever the zombies' attacks lull, the players send out a freelancer, known simply as "bait". The "bait" will attempt to lure the zombies closer to the stronghold, where the trap is set off and the zombie is killed by overwhelming force.
 * Sometimes it is a good idea to commit suicide if your group is under assault by a large horde of zombies. Especially if there are only 2 of you left. Try not using Spike, Plasma, or Firebomb Grenades to kill yourself, because the explosion could damage your teammates. However, this tactic is not recommended in Halo: Reach because suicides also count as being "infected".
 * Try to not use Gravity Hammers or Energy Swords when possible, unless you're very skilled with the weapons, because in most types the zombies have one or both of these weapons and such close range combat would result in you being killed often.
 * A team that regroups in a single area and holds their position in a well defensible location has a much higher chance of surviving.
 * Conserving ammunition is key in all Infection game types, therefore weapons that either fire single shot or bursts such as a Battle Rifle or Carbine are vital if a team is to survive.
 * Accuracy and shot placement are equally important; most players tend to aim for the one spot where it will do the most damage, the head. However, from long range, targeting this part of the body can be tricky, even though the head is less shielded and armored when compared to the rest of the body, it is also a small target. Shooting at the center of mass, the torso or legs, guarantee's better chances of success. In addition, jumping or crouching makes shot placement on the head difficult; the main body isn't as easy to conceal or dodge with.
 * Using hologram can confuse the zombies and make them think they are chasing the player.
 * Never use Armor Lock in an infection game-type. This only makes it easier for the zombies to swarm around you and wait til you pop back up for the kill.
 * Sprint and Evade are also great abilities as they will help you get away from the zombies.
 * Try to avoid using attached turrets where possible, as they leave you unable to move and exposed from behind and to the sides. Only use turrets if you are sure that your team can hold your flanks.
 * The Jetpack can be used to get out of dangerous situations, as well as giving the player the chance to take out the zombies beneath them with headshots from a DMR or pistol. In some maps, the Jetpack can get you to locations the zombies may not be able to reach, thus granting a fairly easy victory.
 * When playing infection on Halo: Reach on Pinnacle hiding out on the 2-story building gives you the best chance to survive.
 * It is common practice for survivors to camp at an exploitable part of the map, where they pick off zombies with relative ease. Though some of these areas have been eliminated through updates, many remain that are simply normal areas of the map that are easy to reach but unbelievably hard to conquer when faced with a strong survivors team.
 * Survivors are not able to pick up ammo, forcing them to pace their shots. In some cases, the last player gets infected before time runs out due to lack of ammo.

Trivia

 * "Infection" is based on the popular custom gametype in Halo 2 known as "zombies". Zombies was based on Team Slayer, with the Red team being humans and the Green team being zombies. The humans could only use human weapons, and the zombies could only use Energy Swords. The game began with just one or two zombie players, who would attempt to hunt down and kill the humans. When a human was killed by a zombie, they would have to change teams and become a zombie. Since there were no facilities in Halo 2 Custom Games to limit what weapons each team could use or to force players to switch teams upon death, zombie gametypes relied on honor rules.
 * New, but simple to obtain achievements are made just for Infection on the Mythic Map Pack, they are Delicious Brains, and Zombie Repeller. Delicious Brains is awarded when the player infects two humans, and Zombie Repeller is awarded by getting two zombie kills as a human.
 * Multiple gametype settings that were available in Halo 3 are absent in Halo: Reach. These include Alpha Zombies, initial zombie percentages, and Next Zombie options.
 * In Halo: Reach, zombie players can be given access to loadouts via the Spartan/Elite Tier 2 loadouts, which are normally specific for Invasion gametypes.
 * It is possible for a human to have an Energy Sword in Halo: Reach, as seen here. For this to happen, a host migration must occur when a human is infected and respawns as a zombie. When the game starts again, there's a chance that the player will turn back into a human, but will keep the zombie loadout.
 * There is a glitch which occurs that causes humans and zombies to betray each other. In Halo: Reach, there is a high chance of a human and zombie killing each other in a close-quarters situation. While this is frustrating, if there is lag present, the kills register after the human has changed teams, leading to the game to count one of the kills as a betrayal. This was why Betrayal Booting was removed from the Living Dead playlist. It is currently unknown how the recent removal of Friendly Fire has affected this occurrence.

Related Pages

 * Alpha Zombie
 * Flood (gametype)
 * Custom games
 * Hide and Seek
 * Save One Bullet
 * Safe Haven