The Infected

Overview
The Infected are a new faction added in the 2.3 Patch. They are basically "zombies" in theme, though Floyd denies that the zombie label is appropriate. They are mutated soilders who went under Empirical experimentation with black nanopods, which irritated their thalamus (part of the brain the deals with pain) whichmade them super aggressive because they believe they are under constant pain.

The Infected generally come in four tiers: Proto, basic (no prefix), Advanced, and Archetype, from weakest to strongest. Colossus instead has 2 forms, Archetype and no-prefix, and players can only control the no-prefix variety. Higher-tier Infected of the same base type will have the same attack options, but have better stats and damage output. Enemy Infected usually have different stats from the player-controllable versions, sometimes stronger, sometimes weaker.

Those who are not squeamish about permanently sacrificing troops can turn normal, non-Nanopod soldiers who are in the Hospital into Infected using a Infection Test Facility. The transformation costs 5 Black Nanopods and takes 8 hours. The results of the transformation are semi-randomized, with more powerful units generally yielding higher-tier Infected.

Biography
The Infected are Imperial soldiers who were subjected to medical experiments involving modified Nanopods. Whereas normal Nanopods can be quite useful for healing the wounded, the modified Black Nanos instead mutated the subjects, causing extensive physical alterations as well as aggression-inducing brain damage.

The Infected have swarmed throughout the Northern Frontier as part of the Infected Outbreak event, launched at the same time as the 2.3 Patch. The end date will be in early November 2012.

Infection
The infection of your own troops works as follows: As we all know by now, thera are 4 total categories which the Infected can turn out into: Proto, "No-Prefix", Advanced and Archetype. Each one of these categories can be reached as the player levels up (this means that for low-levelers under 20 "No-Prefix", Advanced and Archetype Infected will not be available) and the categories are also related to the Troop that is converted. The Infected Levels and Categories are related as follows: Colossus is considered a Level 45 Infected that means that, in order to get one, you have to infect a Bio Grenadier, an Assassinater or a Laser Technician.

To sum it up, here's how you should read the charts!

If you infect a Wimp, Junior Officer, Trooper, Gunner, Riot Trooper, Frontier Pyro, Sharpshooter, Hunter, Grenadier and/or an Arsonist you can get any kind of "Proto" level Zombie;

if you infect an Armadillo, Sniper, Frontier Hunter and/or Ranger you get a "No-prefix" level Zombie;

if you infect a Chemical Trooper, a Peace Keeper or a Demolisionist you get an "advanced" level Zombie;

if you infect a Bio Grenadier, a Laser Technician or an Assassinater you can get an "Archetype" level Zombie, as well as a Colossus!

Current Events
They're back... ( since 2.7 patch) that is to say, they still turn up from time to time around your base at the World map ( Level 27+). Nobody knows if that is a precursor to another zombie event or not.