Infected

Infected is a custom game mode in Call of Duty: Modern Warfare 3 which started as a private match game mode before being released to the online community public playlist on February 5, 2012 for PlayStation 3 and Xbox 360, and on May 9, 2012 for PC.

Gameplay
The game starts with all players being survivors. In the upper left hand corner of the screen, there is a timer that starts with nine seconds counting down to the infected. After the 9 seconds, one player is randomly chosen to be infected. The surviving players must hide from and kill the infected to try and survive until time runs out. The survivors are the players who are not infected, hence the name "survivors". The survivors spawn with an unknown weapon (depending on what the custom settings are) and must survive by killing the infected or hiding. 50 points are given to survivors every time a survivor is infected. The name given with the points is "Survivor". The round ends when the last survivor is killed/infected and the new round will start pending on a new player to be infected.

However, there is a twist in public Infected. Any place where the players will be notoriously difficult to knife by normal circumstances is a 'death zone', wherein a player (including the Infected themselves) will automatically die and join the Infected (if not already). This also applied to Private Matches, but community outburst led to this being reversed in Private Matches. Notable spots include the balcony and signpost by the office in Underground, the blades of the downed helicopter in Bakarra and the van in the loading dock in Arkaden.

Another Infected variant has all the players begin as Juggernauts only armed with .44 magnums dual wielded and Scavenger but nothing else. As before, when the timer is up one player becomes the infected, and gains a Striker as well as keeping the Juggernaut suit. After 1 kill he loses his Juggernaut suit, but retains the Striker, as well as an XM25 and Semtexes. The Juggernauts must kill the infected; if any Juggernaut is slain he will also transfer to the infected team. The Juggernauts win if one person can hold out until the time is up; otherwise victory is forfeited and the infected win.

Class loadouts
NOTE: There are many different class loadouts in the Infected game mode. Not all are listed.

Striker and Five Seven

 * Primary Weapon: Striker (Extended Mags w/ Damage Proficiency)
 * Secondary Weapon: Five Seven (Akimbo)
 * Lethal Item: C4
 * Tactical Item: None
 * Perks: Scavenger, Hardline, Steady Aim
 * Rewards: Sleight of Hand, Quickdraw, Dead Silence
 * Bonus Perks: None
 * Death Streak: None

PP90M1 and .44 Magnum

 * Primary Weapon: PP90M1 (w/ Kick Proficiency)
 * Secondary Weapon: .44 Magnum (Akimbo)
 * Lethal Item: Claymore
 * Tactical Item: None
 * Perks: Scavenger, Quickdraw, Stalker
 * Rewards: Sleight of Hand, Dead Silence, Steady Aim
 * Bonus Perks: None
 * Death Streak: None

FMG-9

 * Primary Weapon: None
 * Secondary Weapon: FMG-9 (Akimbo)
 * Lethal Item: C4
 * Tactical Item: None
 * Perks: Scavenger, Hardline, Steady Aim
 * Rewards: Sleight of Hand, Quickdraw, Dead Silence
 * Bonus Perks: None
 * Death Streak: None

Type 95 and .44 Magnum

 * Primary Weapon: Type 95 (With Red Dot Sight)
 * Secondary Weapon: .44 Magnum (Akimbo)
 * Lethal Item: Claymore
 * Tactical Item: None
 * Perks: Scavenger, Quickdraw, Stalker
 * Rewards: Sleight of Hand, Dead Silence, Steady Aim
 * Bonus Perks: None
 * Death Streak: None

Barrett .50 Cal. and Five Seven

 * Primary weapon: Barrett .50 Cal (Attachments proficiency providing Extended mags and Heartbeat sensor)
 * Secondary Weapon: Five Seven (Akimbo)
 * Lethal Item: Bouncing Betty
 * Tactical Item: None
 * Perks: Sleight of Hand, Hardline, Steady Aim
 * Rewards: Quickdraw, Assassin, Marksman
 * Bonus Perks: Scavenger
 * Death Streak: None

Striker vs Jugg

 * Primary Weapon: None
 * Secondary Weapon: .44 Magnum (Akimbo)
 * Lethal Item: None
 * Tactical Item: None
 * Perks: Scavenger
 * Rewards: None
 * Bonus Perks: None
 * Death Streak: None
 * Juggernaut Enabled

Default

 * Primary Weapon: None
 * Secondary Weapon: Empty USP .45 with Tactical Knife
 * Lethal Item: Throwing Knife
 * Tactical Item: Tactical Insertion
 * Perks: Extreme Conditioning and Quickdraw, Dead Silence granted in some cases
 * Rewards: None
 * Bonus Perk: Lightweight
 * Death Streak: Juiced

Striker vs Jugg

 * Primary: Striker with Extended Mags and Range proficiency
 * Secondary: XM25
 * Lethal Item: Semtex
 * Tactical Item: Tactical Insertion
 * Perks: Sleight of Hand, Extreme Conditioning and Quickdraw
 * Rewards: None
 * Bonus Perk: None
 * Death Streak: Dead Man's Hand

Trivia

 * If the primary and secondary weapons are not selected, the infected have a USP .45 Tactical Knife with no ammo.
 * Infected players do not have specific models and will appear as human soldiers.
 * If the player acquires Juggernaut, infected players will show a unique Juggernaut armor with a black finish instead of the whitish armor.
 * As with Drop Zone, a M.O.A.B. can be achieved, and will wipe out the entire enemy team if used.
 * While playing online, though the infected are sometimes listed to have no third perk, they do not take falling damage, as if they had Dead Silence Pro, though their foot steps can nevertheless be heard. Also, the Featherweight challenges can be achieved this way, even if the player does not have said perk.
 * There are a couple of glitches with the Barrett .50 Cal/ Five Seven loadout, as the infected do actually get Dead Silence in this case. Furthermore, even though the player should theoretically have 2 extra mags with Scavenger Pro, they will begin with the pistols only having 16 bullets (the minimum), and can replenish only by interacting with dead bodies.
 * A Host Migration can occur if the player selected to become infected ends the game, thus causing the network to reboot and randomly choose another person.
 * When one survivor is left, after a few seconds, a UAV is automatically triggered for the infected; however, Assassin will negate the radar scan.
 * The infected move at a faster speed than the survivors.
 * The playlist has been updated multiple times such as adding Throwing Knife, Specialist Strike Package, taking out game modes such as MK46 vs Jug, and removing attachments such as in PP90M1 vs. knife removing Extended Mags.
 * Juiced has no affect on the movement speed of infected players.
 * It is possible to receive negative 50 points for a teamkill by downing an infected with Dead Man's Hand and becoming infected before he explodes.
 * The only way to lose in Infected is to be infected while there are survivors left and time runs out. If the final survivor dies, the player is considered infected and is given a victory.