You can find anything on the Net, including a Zombie Infection Simulation (implemented in Java):
Zombies are grey, move very slowly and change direction randomly and frequently unless they can see something moving in front of them, in which case they start walking towards it. After a while they get bored and wander randomly again.
If a zombie finds a human directly in front of it, it infects them; the human immediately becomes a zombie.
Humans are pink and run five times as fast as zombies, occasionally changing direction at random. If they see a zombie directly in front of them, they turn around and panic.
Panicked humans are bright pink and run twice as fast as other humans. If a human sees another panicked human, it starts panicking as well.
There’s also an advanced version, with humans who catch on to the zombie threat and start to fight back.