Zombie Survival is a modification of Counter-Strike Source, which is very customisable, even enabling you to add new and custom guns for the humans to earn! It introduces a zombie game-mode, where the humans have to survive the round against the zombies, who are made up of their dead team-mates. Humans earn better guns by killing zombies. Zombies can choose from 5 classes, including the explosive chem-zombie, to the strong poison zombie.