The Infected

"I'll see peace back on earth if I've gotta murder every one of these bastards with my own bare goddamn hands!"

- Bill

The Infected are the "zombies" in Left 4 Dead. They are more akin to the zombies from 28 Days Later than to the more popular slow, shambling type. Instead of being dead, they are living humans who have been infected with a mutated rabies virus. There are six varieties of the Infected, four of which are playable. Five varieties are considered "Boss Infected", or "Special Infected", which have special abilities in addition to doing more damage against the Survivors. All AI-controlled Infected are procedurally spawned by the Director.

Common Infected
Common Infected are the most commonly-faced enemy, as well as the easiest to defeat. They are exclusively AI-controlled and fairly weak. Their strength lies in their tendency to attack in large groups of up to several dozen, known as Hordes. While they seem capable of ignoring pain, they can still be killed easily. They are capable of climbing ladders and scaling objects, as well as breaking down weak walls. This type of Infected are attracted by loud noises or bright light.

Hordes
Hordes are large groups of Common Infected that will rush the Survivors at random intervals, after triggering a car alarm or other Panic Event, Crescendo Event, during a Finale, and during the aftermath of a successful Boomer attack.

The Witch


The Witch appears only once or twice per campaign, and is passive unless provoked by flashlights, gunfire, or Survivors in close proximity. She is very powerful, and is capable of killing players with a single attack as well as sustaining much damage before dying. Luckily, many hints are given to let Survivors know when a Witch is nearby. The Witch cries loudly, which Survivors will mention they hear, and dramatic music will play. While the Witch can be killed, it is best to avoid startling her unless absolutely necessary.

The Screamer


The Screamer is a cut AI-Controlled Special Infected that would have appeared one or more times per map. It would wander around until it came in contact with the Survivors. Once it saw them, it would quickly run away and hide. When it was successfully hidden, it would let out a scream that would attract the Horde.

During testing, play testers complained that the Screamer would end up being too hard to spot in a crowd of Infected. Its horde-attracting scream ended up evolving into the Boomer's bile.

A sound file describing the screamer and a picture of the Screamer can be found in the Left 4 Dead Folder, by searching for screamer.vtf, and com-thescreamer.wav.

The Boomer


The Boomer is an Infected that vomits a special bile at Survivors, which blinds them and draws Common Infected to them. At a distance the Boomer is little threat, since he is extremely slow and weak. However, if within range he can vomit on Survivors, attracting the Horde. When he dies, he explodes and covers any Survivors who are close enough in his bile. If a Boomer is killed, nearby Survivors will additionally be blinded, and will stumble backwards. Boomers can be anticipated because of the gurgling noise they make.

The Hunter


The Hunter is similar to the fast zombies from Half-Life 2, although they are not as mutated on the outside. The Hunter is extremely quick and agile, capable of quickly scaling walls. Additionally, he can pounce on players and pin them down, clawing at their abdomen until either the victim is dead, or the Hunter has been knocked off by another Survivor or killed—they are not the most physically adept Infected, having relatively low health, and thus it doesn't take very much to kill them. When the Hunter crouches down in preparation to pounce, it growls, giving it away to any nearby Survivors.

The Smoker


The Smoker is an ambush class who can strangle Survivors with his long tongue, similar to Half-Life ' s Barnacle. The help of another Survivor is required to escape from a Smoker's hold. As the name implies, Smokers emit smoke to impair Survivors' vision and voice communication when killed. A Smoker also will frequently cough, letting the Survivors know when he is in the area. The Smoker can drag players that he has captured with his tongue towards himself, though he remains stationary and cannot move. The Smoker is also momentarily paralyzed for a few seconds after having his tongue removed from his captive by another Survivor.

The Tank


The Tank is the strongest of the Special Infected, though also one of the slowest. However, the Tank can still move as fast as a Survivor, but not when the survivor has full health, and it has outstanding strength and resistance. Despite its generally resilience, the Tank is highly flammable, and when set on fire, it will die within 40 seconds. When controlled by a player, the Tank has a frustration meter that goes up whenever the Survivors aren't in view. Unless the player is able to locate the Survivors and hit them, the meter will continue to fill, and once it is full, the player will lose control of the Tank. The Tank is capable of throwing large objects (such as blocks of concrete, cars, or tree trunks) with sufficient force to momentarily stun Survivors, or even incapacitate them instantaneously. The Survivors are alerted to the approach of a Tank by dramatic music, and the loud pounding a Tank makes when it runs. You will know that a Tank is dangerously close by when the screen starts to shake.