Anonymous is a loosely associated computer " hacktivist " group responsible for many of the major politically motivated cyber attacks that have occurred over the last few years. Since its inception on the imageboard 4chan in 2003 as a joking referral to the name "Anonymous" assigned to each user's post, Anonymous has perpetuated their opposition of Internet censorship through both physical and cyber protests as an anarchistic decentralized body.
As Anonymous is completely decentralized and has no leadership or ranking system, anyone can "join" by simply wishing to do so. Protests and cyber attacks are coordinated by means of imageboards, forums, wikis, IRC, YouTube, and social networking services and any member of Anonymous can organize events as a means of working towards a set of their own goals parallel to the "Anonymous" agenda.
In cyberspace, Anonymous' attacks are often perpetuated through the distributed use of flooding tools such as LOIC (Low Orbit Ion Cannon) and its newer cousin HOIC (High Orbit Ion Cannon). By recruiting a large number of users to voluntarily participate in such attacks (usually over IRC as it is a more anonymous means of communication), Anonymous effectively creates a "voluntary botnet" of hundreds or thousands of computers. Using a vast number of machines running LOIC or HOIC to target a fairly large server will often result in server instability or potentially denial-of-service, making Anonymous formidable as a cyber attacker. Despite this use of "voluntary botnets," much of Anonymous' firepower in some of their most notable attacks came from the use of large botnets owned by high ranking Anonymous members or their friends.
In recent years, some of Anonymous' cyber attacks have included Operation Payback , Operation Blackout , Operation Defense , and some involvement in Operation AntiSec among many others. Anonymous appears in TIME Magazine's 2012 version of their "The 100 Most Influential People in the World" list.