Update: Posted on 23 April by James Gallagher – Blog Manager, SCEE

An external intrusion on our system has affected our PlayStation Network and Qriocity services. In order to conduct a thorough investigation and to verify the smooth and secure operation of our network services going forward, we turned off PlayStation Network & Qriocity services on the evening of Wednesday, April 20th. Providing quality entertainment services to our customers and partners is our utmost priority. We are doing all we can to resolve this situation quickly, and we once again thank you for your patience. We will continue to update you promptly as we have additional information to share.

http://blog.eu.playstation.com/2011/04/23/update-on-playstation-network-qriocity-services/

Posted on 21 April

Reports are coming in that 'hacktivist' collective Anonymous may have made good on their promise to mount the "biggest ever" attack on Sony's PlayStation network (PSN), as company engineers are investigating the possibility that the online gaming service has been downed by outsiders.

James Gallagher, blog manager for Sony computer Entertainment Europe, posted the following as Sony engineers struggled to end the unexpected outage which had previoulsy been attributed to "routine maintenance":

As you are no doubt aware, the current emergency outage is continuing this afternoon and all Sony Online Network services remain unavailable. Our support teams are investigating the cause of the problem, including the possibility of targeted behaviour by an outside party. If the reported Network problems are indeed caused by such acts, we would like to once again thank our customers who have borne the brunt of the attack through interrupted service.

 Sony PlayStation websites are down too

Anonymous takes down Playstation website and Playstation Network Once Again

no it sony annoymous said he going to attack when psn back on in a few days

nah apparently it's an issue from Japan

After spending about 20 minutes in the Anon irc chat today, I can say they had nothing to do with it.

So what's the deal with Anonymous, why would he want to attack Sony? Is it because of the whole Geo Hot thing?

No, it's because of the whole living in mom's basement, never having seen a naked woman thing.

Speaking of which, My C.viper misses whooping you around. whenz we gonna playz? D:

I think that jumping to the conclusion that it was anon is wrong. They have already admitted that such attacks were harming the customers more than they were harming Sony, and thus said they would stop.

Edit - saying things without sources? I'm almost as bad a journalist as whoever wrote that article linked in the OP. Here you go, boys and girls

http://www.eurogamer.net/articles/2011-04-14-anonymous-biggest-ever-attack-on-sony

Whats funny, is that if it annoymous they have lost support of alot of people, also sony is most likely saving money on the Massive Power bills that running an network of such size is. 

sony is having issues in japan. I wonder if it has anything to do with the latest quake there?