Left 4 Dead

Left 4 Dead 

Is a firts person shoter. In campaign mode, the player takes control of one of the survivors; if four human players are not available, then the remaining survivors are AI-controlled bots. They play through the levels fighting off the infected—living humans who have been infected with a rabies-like virus that causes psychosis. The survivors are carriers of the disease, so they do not show signs of any symptoms.