Zombie (computing)

A zombie computer (often shortened as zombie) is a computer attached to the Internet that has been compromised by a hacker, a computer virus, or a trojan horse. 
Generally, a compromised machine is only one of many in a botnet, and the hacker will make the computer do unwanted things from far away. Most owners of zombie computers do not know that their system is being used in this way. Because the owner tends to not know, these computers are compared to zombies.