A botnet is a set of infected computers that, without the knowledge and consent of proprietaries, are configured to transmit data, information, spam or virus towards other computers connected to the Internet. The bot prefix indeed comes from the fact that any infected machine becomes a "slave" of the controller, called botmaster, that can run remote commands.

The main use of a botnet is about realizind Denial of Service attacks towards specific objectives and the diffusion of spam and phishing campaigns.