Anonymous is an organization standing against all kinds of censorship on the internet. They were started as a small number of activist hackers. Now, they are highly popular among every state in the world. Anonymous are known as their attacks to government, religious, cooperation web sites. “In its early form, the concept was adopted by a decentralized online community acting anonymously in a coordinated manner, usually toward a loosely self-agreed goal, and primarily focused on entertainment, or “lulz“.” (wiki)
After 2008, the organization started to take active roles in protests against authorities and religious movements. Anons (members associated with Anonymous) publicly supported WikiLeaks, created Pirate Bay (an internet site where you can download movies, games, tv shows), hacked official government sites of U.S, Israel and much more. They are associated with Guy Fawkes mask, it is pretty much their symbol. Lots of people got arrested because of involving in Anonymous actions.