“Bots” refer to programs that reside on a computer and provide remote command and control access via a variety of protocols, including IRC, HTTP, instant messaging, and peer-to-peer protocols. When several of these bots are under common control, it is commonly referred to as a botnet. Bots provide the controller with features that can be used to support illicit activity, including :

1. Relays for sending spam and phishing emails
2. Web servers or redirectors for spam/phishing sites or malware distribution
3. Updates for existing malware
4. Installation of additional malware
5. Distributed denial of service (DDoS)
6. Proxy services
7. Pay-for-click services
8. Vulnerability scanning and exploitation
9. Surveillance

In addition to the ability of most bots to infect new hosts through built-in scanning and exploitation of  vulnerabilities, bots can also be deployed through social engineering techniques. These include mass mailing, file-sharing programs, and instant messaging networks.