Zombies

The infected, also known as "zombies", "zeds" or "deadbrains", were first noticed in the crowded cities of San Andreas days after the earthquake: crazed humans trying to rip apart anybody or anything with a pulse. Nobody thought of them to be 'zombies' at first. Since the world was already in a bad state, with armed gangs rampaging the streets and panicked refugees gathering in the few government safe camps, a few random acts of ultra-violence did not caught attention. This only facilitated the spread of the infection and when the officials finally acknowledged the epidemic, it was too late to be stopped.

Zombie types
Four types of the infected were observed so far:
 * Walkers are the most common type of zombie. They only walk around during the day, but become more alert at night and are able to run after players and climb obstacles to get them. Some walkers have the ability to transform into a ‘runner’ upon player detection.
 * Runners are slender hungry zombies, more aggresive and infectious than walkers and brutes. They will sprint after their prey for as long as they need to and will employ evasive maneuvers when shot at. They can usually be encountered in larger numbers outside of the large cities. A useful tactic against runners is to get the higher ground or jump over obstacles and pick them up as they climb.
 * Brutes are the strongest infected variety, zombies that recently fed in copious amounts. The virus efficiently converts the flesh they eat into overgrown muscles and fat deposits that protect the body. As a consequence, they can not be headshot, but they also can't climb over obstacles. Brutes have a stomping special attack that will temporarily incapacitate targets. Each time you damage a Brute, there's a small chance it will get frenzied and morph into a Rammer.
 * Rammers are highly dangerous foes. Combining the strengths of both the Brute and the Runner, they employ a very fast medium range charging attack that can pin down survivors and kill them in seconds.

Infection
Not much information is publicly available about the infection to this day. The 'zombie disease' seems to spread through body fluids like saliva and blood and has a short incubation period before altering the brain forever.

The metabolism of the infected seems to be modified by the virus, allowing them to bear large periods of time without feeding. The hungrier they get the more aggressive they become.

They are more resistant to bodily harm than uninfected humans and have seemingly unlimited stamina, but can be slowed down by well placed shots to the legs and chest. Headshots are (mostly) still lethal.

They are disoriented by the light, so days are slightly safer than the nights. During the night, regular Walkers will have heightened senses and move at same speed as Runners.

If you are caught off guard by a zombie that sneaks to your back, you can be forcefully grabbed and infected.

Infection has three stages. The first stage can be taken for a regular flu as it has the same symptoms. Second stage will add more severe symptoms like blurred vision and dificult coordination. The third, final stage, will start depleting your health. This final stage ends only when you are dead or cured.

Cure
The only known cure for the infection - the ZomboKleenTM pills, ZK for short - can be found in the vaults of Zombotech Corporation, but prepare yourself for a fight, as countless zombies swarm the place.

Detection
Zombies react to gunshots and other human activity noise, rushing to the position of the sound. They can be sneaked upon by crouching, as long as you don't get too close. Alerting one zombie might alert other zombies that are in his range.