Anonymous is an international activist group of hackers who are quite popular for their cyberattacks on several governments, government institutions and government agencies, corporations and the Church of Scientology.
The movement was formed in 2003. Though a decentralized community, Anonymous members, referred to as anons, can sometimes be spotted in public by the wearing of Guy Fawkes masks in the styles portrayed in the graphic novel and film, V for Vendetta.
How to join anonymous?
Since anonymous is a decentralized group, you don’t sign up per se. There’s no membership registration or group. You simply need to facilitate a connection and the interwebz will offer you all the information you need.
There is no specific group for anonymous hackers or otherwise to join.
Anonymous is more of an idea that aims at freeing humanity from the followers of greed in government, government agencies and the likes.
You automatically join anonymously if you believe in the idea and are willing to help manifest it through whatever means necessary.