Anonymous

Anonymous is a loosely organized hacktivist collective created to promote free speech, unimpeded access to information, and transparency in government and corporate activities. A The collective's slogan "We are Legion" refers to both the group's numbers and the anonymity of its members.
Anonymous comprises a diverse group of individuals connecting through social networking sites, forums and blogs scattered all over the world. Although the group was initially known for online pranks, it has become more serious and political in recent years.
Activities of Anonymous have included the following:

• In December 2010, Anonymous targeted the websites of organizations that it considered hostile to WikiLeaks or its founder Julian Assange.
• In August 2011, Anonymous sent out a mass email/fax bomb to San Francisco Bay Area Rapid Transit's personnel and organized multiple protests at the network's Civic Center station, in response to a shutdown of cell phone service. The shutdown was an attempt to prevent the organization of a non-violent assembly protesting a police shooting.
• In October 2011, the collective took down 40 child pornography sites, published the names of over 1500 users of those Web sites, and suggested that the FBI and Interpol follow up.
• Throughout the latter half of 2011, the group was also involved in the organization and support of the Occupy Wall Street movement.
• In January 2012, the collective attacked the United States Justice Department, as well as those belonging to several major entertainment industry organizations. The attack was in response to the government's seizure of Megaupload, a locker service that allows anonymous file transfers.
• In April 2012, Anonymous took several U.K. government websites offline, as a protest against what it called the country's "draconian surveillance proposals" and "derogation of civil rights." The denial of service (DoS) was a response to the proposed "Patriot Act," which would allow government monitoring of all phone calls, emails, social network and Web traffic.

MORE INFO:
> Anonymous attacks: Three phases of an anonymous attack methodology