SONY has finally admitted outside hackers are responsible for a major PlayStation Network disruption.

The network outage, which began four days ago, is affecting more than 70 million users worldwide, who use it to play video games against friends online, stream movies and shop online.

Players can still play games offline, but are unable to challenge others over the internet, one of the console's key features.

"An external intrusion on our system has affected our PlayStation Network and Qriocity services," Sony senior director of corporate communications and social media Patrick Seybold said in an online post, confirming for the first time that hackers had played a part in the shutdown.

"We are doing all we can to resolve this situation quickly, and we once again thank you for your patience," the statement added.

Sony said that it had shut the network down voluntarily "in order to conduct a thorough investigation and to verify the smooth and secure operation of our network services going forward."

No information was given on when users could expect the service to be restored.

Hacker group Anonymous was originally suspected of causing the disruption as it had previously vowed retribution against the Japanese electronics giant after it took legal action against two hackers.

However, in a message on its website Friday entitled "For Once We Didn't Do It," the group denied responsibility, saying that while it was possible that individual hackers had targeted the network, Sony wasn't an official target.

The message went on to accuse Sony of "taking advantage of Anonymous' previous ill-will towards the company to distract users from the fact that the outage is actually an internal problem with the company's servers."

The outage came during a heavy playing week in the United States, with many public schools closed for spring break and an Easter holiday providing an opportunity for an extended weekend.