Gamers frustrated as Sony PlayStation network remains down for third day amid hacking claims

The same Twitter account was also used in August to make an apparently false report that a bomb was on an aircraft carrying a Sony executive.

So far there is no specific evidence to link the episodes with last month's malware attacks on Sony's film division. The current episode does not appear to have exposed any corporate or customer data, but one expert said the Lizard Squad group was capable of serious disruption.

"They're well-practised and, from what I see, they've got the capability to take down a lot of things," said Dan Holden, director of security research for Arbor Networks, a cyber-defence company based in Burlington, Massachusetts. He said little was known about the group or where its members were based.

"Their cause is a little bit oddball," said Mr Holden, adding that the group appears to be motivated primarily by a desire for visibility and "lulz" - internet slang for laughs. Mr Holden said he recently described them on his blog as "hacktivists" or online political activists, until the group contacted him on Twitter and asked to be called "cyber-terrorists".

He said the attacks caused economic damage to gaming companies. "It's certainly costing money all the way around to defend against these attacks," he said, adding that Sony may also face the wrath of customers whose brand-new PlayStations would not work on Christmas Day.

Lizard Squad's claimed attack on Sony's gaming network last summer has also prompted speculation it might be involved in the November hack of Sony Pictures Entertainment, which the FBI has blamed on North Korea.

While experts say it is possible the North Korean government worked with independent hackers, Mr Holden also noted that Lizard Squad Twitter accounts appeared to applaud the internet outage that afflicted North Korea this week.

"It's totally speculative," he said of suggestions that Lizard Squad might be involved in the Sony Pictures attack.

Meanwhile, someone using a Lizard Squad Twitter account claimed the group was shifting its attention to attack a widely used internet encryption service called Tor.

Later a Tor spokeswoman said the service was responding to an attack but did not expect any "performance effects".