What Anonymous isn't.
There are two things you need to understand right off the bat before any productive discussion of the Sony Hack and Anonymous can continue.
1. The single person or small group who perpetuated the Sony hack are very likely "members" of Anonymous.
2. This does not mean that Anonymous, the organization, had anything to do with the Sony hack.
These people are not master criminals.
Let's start by asking 'What is Anonymous?'. There is a lot of erroneous information about the group's methods, organization and capability. Some misinformation comes from mischievous elements within Anonymous, and the rest comes courtesy of hyped-up news reports. There are a number of different, highly situational definitions of just what 'Anonymous' is. But here's what they aren't.
An elite hacking super-group.
Some sort of cult.
The Internet's Mafia.
They might be the Internet's best poster-makers, though.
I'll address each of these misconceptions separately.
They're hackers! SUPER-hackers! They beat Sony, AND the security firm HBGary. Anonymous is many thousands of people. The single, solitary membership requirement is that you decide you want to be counted as one of Anonymous. There's no registration required, no payments needed and no secret membership ritual. It is absolutely true that a small fragment of Anonymous are skilled hackers, but that does not mean they coordinate their doings with the larger bulk of the group. Or even each other.
The sort of hackers who steal credit card data (the vast majority of 'hackers' are perfectly ethical people) are committing a serious criminal act, and they know it. These people are risking prison time. Sony noted that they took great pains to cover their tracks. And they certainly timed their attack along with Anonymous' DOS assault on Sony, but you're naive if you think anyone outside the people responsible for the hack knew it was coming.
Blaming Anonymous for the Sony hack makes about as much sense as blaming the student body of UT Austin for the Clocktower Sniper's rampage. Anonymous has a lot of gamers, and I've no doubt many thousands of them ended up losing their credit card info too. No one ever seems to consider that.
Terrorists. This accusation actually has a little merit to it. Members of Anonymous have stalked little girls and waged bizarre wars of intimidation against a dizzying array of targets. But all of the group's larger projects have had a strong sense of social justice to them. They went after PayPal and those credit card companies for freezing donations to Wikileaks. HBGary is a ridiculously shady company I can't quite blame Anonymous for going after them. Sony was targeted- with nothing but a DOS attack- because they chose to sue a man for hacking his PS3 and posting a guide online.
Some people deserve being rampaged at.
Anonymous is not blameless. They are not heroes. But they aren't malicious demons either. Most of them are kids in their teens and twenties, who downloaded the Low Orbit Ion Cannon or attended a protest because they thought it would be neat to be a part of something for a little while.
Some sort of Cult / The Internet Mafia People tend to think of Anonymous as some sort of cyber army or cult or Internet Mafia. Using any of those terms credits the Anons with far more organization than they actually have. For example: AnonOps is currently in the midst of a Civil War. A "rogue admin" has gained control over several of their organizing sites.
I'm still about 40% sure this is a joke. But with the Internet, there's really no telling.
Anonymous is just organized enough to orchestrate mass DOS attacks, but they only really have power when they're riled up. If a situation bleeds drama, if the news agencies flock to it and the people fret over it and the target of their rampage tries to fight back- that gets Anon interested. That keeps thousands of people flooding back, day after day, to press the fight. That's how you get crowds of people in masks and week after week of new stories.
It's sort of like the Streisand effect. Responding to Anonymous only makes them more eager to go after you.
So Who IS Responsible for the Sony Hack?
The best I can give you is an educated guess, but here it is: A small group of very skilled people, possibly a single person, followed the planning for Anon's DOS attack on Sony and waited until then to spring into action. The responsible parties probably had a buyer for the stolen data- I doubt the people shopping around "credit card data" in hacking forums are legitimate. This buyer is almost certainly foreign.
While one or more of the attackers were likely "Anons", they planned and executed this hack on their own. That 'calling card' was left as sort of a red herring, to focus attention on a giant, well-publicized group and keep it off the responsible parties for as long as possible. The hackers may have had some ideological issue with Sony, but their primary motivation was financial in nature.
I sincerely hope that the guilty parties in this attack will be brought to justice soon. But blaming Anonymous for the theft of that private data is pointless and inaccurate. The people worth being angry at are the few hackers responsible, and the Sony executives who decided their archaic, ailing security was enough to keep 77 million people safe.