Botnet is a term derived from the idea of bot networks. In its most basic form, a bot is simply an automated computer program, or robot

In the context of botnets, bots refer to computers that are able to be controlled by one, or many, outside sources. An attacker usually gains control by infecting the computers with a virus or other malicious code that gives the attacker access

Your computer may be part of a botnet even though it appears to be operating normally. Botnets are often used to conduct a range of activities, from distributing spam and viruses to conducting denial-of-service attacks