Definition: Botnets are groups of computers connected to the Internet that have been taken over by a hacker. The hacker controls all the computers and they behave like a “robot network” (a.k.a. "botnet"). Bonets contain anywhere from hundreds to thousand of computers. The botmaster (the hacker who controls the botnet) then uses these computers to send spam email, spread viruses, attack other networks or any other variety of malicious activity.
Also Known As: Bots, zombies, zombie army
Examples:
If your computer is hacked and becomes part of a botnet you may not even know it.