The Infected are zombies and the main enemies of the game. The Fearless, Tireless, Relentless, Numberless, Merciless infected used to be humans in the past until a mutated form of rabies, called Rabies Z turned them into mindless zombies. Now they make up a majority of the world's population with wandering swarms constantly hunting for the last remaining humans.
Large groups of infected occupy a majority of the map with entire swarms concentrated around Villages of Doom. Any infantry unit or building that gets too close to the infected will attract their attention. They also react to the noises made by weapons and the behaviors of other infected around them.
If even a single infected deals enough damage to a building (one hit is enough once the defensive barrier is removed) with workers or colonists, the building becomes infected and its inhabitants will turn into zombies potentially resulting in an outbreak that will spiral out of control if not immediately taken care of. The number of infected spawned from such buildings differs from one building type to another.

All Infected have 100% Venom Resistance and have no friendly fire.
| Types of Infected ⇅ | Column 2 ⇅ | Column 3 ⇅ |
|---|---|---|
| Walkers | Infected Aged Infected Decrepit Infected Young | Low-level Infected that are the very first you will encounter, they have a very slow movement speed and low health. These Infected, while weak, make up for it in numbers. There are thousands placed around the map and if provoked can create a swarm early in the game that can be hard to repel. |
| Runners | Infected Colonist Infected Fresh Infected Executive | Mid-level Infected found in Villages of Doom, at medium distance from spawn and as part of swarms. They're fast and can pose a significant threat. |
| Special Infected | Infected Chubby Infected Harpy Infected Venom Infected Behemoth Infected Giant | Rare, high-level Infected found close to the edges of the map, in Villages of Doom or as part of late-game swarms. They possess unique abilities making them a huge threat to even heavily defended colonies.Infected Giants only appear at difficulty "Medium Population (Challenging)" and higher. |
| Infected Type ⇅ | Hit Points ⇅ | HP Regen ⇅ | Armor ⇅ | Move Speed ⇅ | Attack Range ⇅ | Attack Damage ⇅ | Attack Speed ⇅ | Watch Range ⇅ | Attack Noise ⇅ | Experience ⇅ | Notes ⇅ |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Walkers | 35 | 3 | 0% | 0.4 | 0.5 | 6 | 1 | 5 | 1 | 1 | The group consists of Aged, Decrepit, Young. |
| Fresh | 45 | 4 | 5% | 1.75 | 0.6 | 10 | 1 | 6 | 2 | 2 | |
| Colonist | 45 | 4 | 5% | 1.75 | 0.6 | 9 | 1.11 | 6 | 2 | 2 | |
| Executive | 80 | 7 | 10% | 1.75 | 0.6 | 12 | 1.25 | 6 | 3 | 5 | |
| Harpy | 120 | 10 | 10% | 5 | 0.8 | 30 | 3.33 | 9 | 10 | 10 | Can jump over walls.Very sensitive to noise. |
| Venom | 120 | 10 | 10% | 1.75 | 4.5 | 30 | 0.5 | 8 | 10 | 10 | Ranged AoE attacks. |
| Chubby | 500 | 20 | 15% | 1.75 | 0.7 | 40 | 1 | 5 | 10 | 10 | |
| Giant | 4,000 -20,000 | 50 | 30% | 4 | 3 | 160 | 1.25 | 10 | 20 | 100 | Very large AoE attacks.Deaf (attracted only by sight/damage). |
| Behemoth | 1,500 -8,000 | 320 | 10% | 6 | 2 | 30 | 2 | 12 | 200 | 50 | Large AoE attacks.Extremely sensitive hearing. |