This is the only true piece of information in this thread.
Anonymous is a group originating from the murky depths of 4chan. As PF said, it isn't exactly a group. it's an idea. The idea coming from the basis of 4chan itself, how every user is considered anonymous. The more active members use this anonymity to voice their personal opinions through this 'Anonymous' scapegoat, sometimes acting upon them with protests or hacking raids. They don't just hack any average joe, because they are the average joe. They're a sort of internet vigilante, acting on those who do the wrong thing, such as the scientologists, the Westboro Baptist Church
I'm no fanboy, the general populace of anonymous now are children ruining their image, such as empty threats as we have just seen.