A voluntary botnet is a distributed network of computers whose processing power is harnessed to steal data or carry out a political or socially-motivated denial of service (DoS) attack.
Most botnets are created without the knowledge of the co-opted computers’ owners. Voluntarily participating in a botnet with the intention of shutting down a web site or stealing data is a violation of most Internet service provider (ISP) terms of service as well as the United States Web Computer Fraud and Abuse Act.
Voluntary botnets drew public attention in 2010 when a hacktivist group called Anonymous solicited volunteers to bombard the websites of organizations, businesses and governments whose policies the group found offensive. The group urged supporters to voluntarily download and install a client-side open source network stress testing application called Low Orbit Ion Cannon (LOIC). The application has a mode called HIVEMIND which can connect the client to an Internet relay chat (IRC) server, allowing the Anonymous webmasters to control the volunteer's computer remotely.
The term voluntary botnet should not be confused with the term "voluntary computing." Voluntary computing applies the principles of grid computing in a positive way to create a distributed network capable of processing data for research projects. A voluntary computing network is sometimes called a white hat botnet.