We've been hacked: Sony finally blames 'external intrusion' for PlayStation Network outage

After almost four days of disruption, Sony has admitted that outside hackers are responsible for a major PlayStation Network outage.

But mystery still surrounds who is responsible - as the primary suspect, the Anonymous group, has denied all responsibility.

The outage, which began on Wednesday, is affecting more than 70 million gamers worldwide, who use the network to play video games against friends online, stream movies and shop.

Sony has admitted that 'external intrusion' - or hacking - has led to the shutdown of PlayStation Network

Gamers can still play on the site but they cannot challenge others to play with them - a major component of the network.

Patrick Seybold, Sony's senior director of corporate communications and social media, released an online post apologising for the outage, and admitting the breach of security.

He said: 'An external intrusion on our system has affected our PlayStation Network and Qriocity services.

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

We didn't do it: Members of the hackers group Anonymous, with their trademark masks, at an event in Los Angeles. The group has denied all responsibility for the Sony shutdown

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'.

But the statement made it clear that a hacker or hackers were instrumental in the network's shutdown.

The finger of suspicion pointed to the Anonymous group, which has publicly vowed vengeance for the company taking legal action against two hackers, including George Hotz.

But the group, which also has connections to WikiLeaks, has said it had nothing to do with the intrusion.

In a statement on its website, Anonymous said: 'For once we didn't do it.'

It 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'.

While there is clearly work being done from outside, Experts are starting to believe that Anonymous is telling the truth.

PCWorld's Keir Thomas said the phrasing Sony used - talking of an 'external intrusion' - indicated that the attack wasn't a Distributed Denial of Service (DDoS) attack, which is one of Anonymous's most popular weapons.

He wrote: 'Instead, this seems to be an individual breaking into the network and this is probably why it's taking so long to clean-up - Sony has to trace every corner of their systems affected by the hacker and repair it or restore files.'

Sony has not said when users could expect to have their network back.