PlayStation Network confirms that an attack caused the service outage (PSN down)

PlayStation Network service still down, and the official PlayStation Blog has confirmed that the cause was an attack they suffered in their systems, affecting the PSN and Qriocity services.

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.