Looking at the timeline.................
2 April: Anonymous, the online activist collective, begins Operation: Sony, a series of denial of service attacks on Sony websites that it says are in defence of free speech.
11 April: Sony announces the case has been settled out of court and that George Hotz has agreed to take down his website.
13 April: Anonymous says it will intensify its attacks and calls for a day of protest on 16 April. “In the eyes of the law, the case is closed, for Anonymous it is just beginning… prepare for the biggest attack you have ever witnessed, Anonymous style,” it says in a video message.
16 April: Hackers break in to Sony Online Entertainment, the firms PC gaming service and steal 25 million users’ personal details. Around 23,400 European users’ credit card or direct debit details may also have been taken.
17 April: Hackers break in to the PlayStation Network and steal 77 million users’ personal details.
19 April: Sony detects the PlayStation Network breach.
20 April: Sony shuts down the PlayStation Network, publicly citing technical problems.
26 April: Sony publicly discloses the PlayStation Network breach and says it has called in the FBI.
1 May: Investigators discover the breach of Sony Online Entertainment and Sony shuts it down. Separately, Japanese Sony executives bow in apology for the PlayStation Network breach.
2 May: Sony publicly discloses the Sony Online Entertainment breach.
4 May: Kazuo Hirai, Sony’s chairman, tells a US Congressional committee that the hackers left a calling card implicating Anonymous. Investigators found a file named “Anonymous” with the motto “We are Legion. He also says the collectives denial of service attacks made it easier for the hackers to breach security.
“Security teams were working very hard to defend against denial of service attacks, and that may have made it more difficult to detect this intrusion quickly - all perhaps by design,” Mr Hirai says.
4 May: A press release purporting to come from Anonymous denies credit card theft but does not directly deny hacking Sony’s systems or stealing personal data.
“We are trying to fight criminal activities by corporations and governments, not steal credit cards,” it says.
.........Anonymous would naturally be prime suspects IMO!