Botnet

A bot or web robot is an automated malware program that scans blocks of network addresses and infects vulnerable computers. This type of program allows hackers to take control of many computers at the same time and turn them into bots (also known as a zombies). Hackers typically use bots to infect large numbers of computers. This large group of infected computers is referred to as a botnet. If your computer is infected and becomes a member of a botnet, it can be used in distributed denial of service (DDoS) attacks, and can also be used to perform automated tasks over the Internet unbeknownst to you (for example sending spam, viruses or stealing personal and private information such as bank credentials or credit card numbers).

For more information see Virus radar.