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.

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.

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

Striker

 * Primary Weapon: Striker (Extended Mags w/ Damage Proficiency)
 * Secondary Weapon: Five Seven (Akimbo)
 * Equipment: C4
 * Perks: Scavenger, Quickdraw Pro, and Steady Aim Pro

PP90M1

 * Primary Weapon: PP90M1 (Extended Mags w/ Kick Proficiency)
 * Secondary Weapon: Five Seven (Akimbo)
 * Equipment: Claymore
 * Perks: Scavenger Pro, Quickdraw Pro, and Steady Aim Pro

FMG-9

 * Primary Weapon: FMG-9 (Akimbo)
 * No Secondary Weapon
 * Equipment: C4
 * Perks: Scavenger, Hardline, Steady Aim

Type 95

 * Primary Weapon: Type 95 (Red Dot Sight and Rapid Fire w/ Attachments Proficiency)
 * Secondary Weapon: Desert Eagle (Akimbo)
 * Equipment: Claymore
 * Perks: Scavenger, Quickdraw, Stalker

Striker vs. Juggernaut

 * Primary Weapon: .44 Magnum akimbo
 * No Secondary Weapon
 * Equipment: none
 * Perks: Scavenger
 * Juggernaut enabled

Barrett .50 Cal.

 * Primary weapon: Barrett .50 Cal (Extended mags and Heartbeat sensor w/ Attachments proficiency)
 * Secondary Weapon: Five Seven (Akimbo)
 * Equipment: Bouncing Betty
 * Perks: Sleight of Hand pro, Quickdraw pro, and Steady Aim pro

Default

 * Primary Weapon: USP .45 (NO AMMO) (Tactical Knife)
 * Secondary: NONE
 * Lethal Equipment: Throwing Knife
 * Tactical Equipment: Tactical Insertion
 * Perks: Extreme Conditioning Pro and Quickdraw Pro
 * Bonus Perk: Lightweight
 * Death Streak: Juiced

Striker vs. Juggernaut

 * Primary: Striker Extended Mags
 * Secondary: XM25
 * Lethal: Semtex
 * Tactical: Tactical Insertion
 * Perks: Sleight of Hand, Extreme Conditioning and Quickdraw
 * 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.
 * Just like in Drop Zone, a M.O.A.B. can be achieved.
 * While playing online, though the Infected are not listed to have a third perk, they do not take falling damage, as if they had Dead Silence Pro, though their foot steps can still be heard. Also, the Featherweight challenges can be achieved this way, even if the player does not have them unlocked. (This does not happen when the Survivors loadout contains Barrett .50 Calibers, as the Infected do actually get Dead Silence in this case.)