Common Infected are the most frequently faced members of the Infected, and the easiest to defeat. Their strength lies in the fact that they attack in groups, more commonly referred to as The Horde, sometimes as large as several dozen.
The Special Infected have been heavily mutated by the Infection, giving them "special abilities." Each generally has a unique ability that a Survivor cannot face alone, making them the true teamwork testers in this game. They are not attracted by car alarms or loud noise and have a higher degree of intelligence than Common Infected. They are the only infected that are playable in Versus mode.
The Uncommon Common Infected are new forms of the Common Infected introduced in Left 4 Dead 2. They have the same general weaknesses but have slightly higher health than most Common Infected and have an immunity to a certain weakness (such as fire or headshots) of a Common Infected.
- Fallen survivor infected
- Clown infected
- Mud men infected
- Swat (Called Riot) infected
- Worker infected
- CEDA Worker infected
Known Infected Individuals
- Carolyn: Turned into common infected after minutes of being bitten by from infected guy.
- Jimmy Gibbs Junior: Turned into common infected (period of time unknown).
- Lt. Mora : Turned after a few minutes, he was in transition of turning and was still able to hold a gun and speak some English; however, he sees survivors as monsters (might not have been completely turned).
- News Chopper 5 Pilot: Turned into Common Infected in mid-air after rescuing and encountering the Survivors. He was bitten prior to rescuing the Survivors, which resulted in Zoey shooting him as soon as he turned.
- Sandra: Turns into a Common Infected (period of time unknown).
- The Church Guy: turns into either a Special Infected (Boomer, Hunter or a Smoker) after one hour of being bitten.
- Helicopter Pilot (Left 4 Dead 2): Turned into Common Infected in mid-air after rescuing the Survivors, which caused Nick to shoot him.