SAN FRANCISCO » Sony’s PlayStation network remained offline Friday on the second day of an outage that began roiling the online world just as eager video game players were unwrapping new consoles on Christmas morning.

Microsoft’s Xbox Live service, which also went down Thursday, was back online Friday although the company reported reported problems with some functions in the afternoon.

Credit for the disruptions was claimed on Twitter by a group of self-proclaimed hackers called Lizard Squad — or someone purporting to speak for the group. But many video game enthusiasts and some other hacker groups quickly condemned their actions. Even the notorious Kim Dotcom, a New Zealand-based online entrepreneur who’s been accused of abetting Internet piracy, got into the act by offering free vouchers for his online privacy service if the Lizard Squad would agree to restore the Xbox network.

A Lizard Squad account on Twitter appeared to credit Dotcom’s offer for the partial restoration of Xbox service on Friday. But exactly what happened is still unclear: Neither Sony nor Microsoft would say what disrupted their networks. And experts say it’s difficult to trace the source of attacks or confirm claims of responsibility.

Sony Online Entertainment said on its website Friday that its Playstation network was still down, adding on Twitter: "We are working to restore full network services for all platforms – thanks, as always, for your patience!" A Microsoft support site said Xbox Live was available at midday Friday, but it reported new problems in the afternoon.

Signs of trouble emerged earlier this month when someone using a Lizard Squad account on Twitter began threatening to disrupt gaming services on Christmas — and then boasted of causing the outages on Thursday.

A person or group using the same name on Twitter took credit last August for similar attacks in which hackers overwhelmed company servers with a flood of Internet traffic, disrupting the online gaming networks operated by Sony, Riot Games and other companies. The same Twitter account was also used in August to make an apparently false report that a bomb was on an airliner carrying a Sony executive.

So far, there’s no specific evidence to link these episodes with last month’s malware attacks on Sony’s movie division. The current episode doesn’t appear to have exposed any corporate or customer data. But one expert said Friday that the Lizard Squad group is capable of serious disruption.

"They’re well-practiced 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-defense company based in Burlington, Massachusetts. He added that little is known about the group or where its members are based.

"Their cause is a little bit oddball," said Holden, adding that the group appears to be motivated primarily by a desire for visibility and "lulz," which is Internet slang for laughs. 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."

Holden said the attacks did cause 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 ire of customers whose brand-new PlayStations wouldn’t 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’s possible the North Korean government worked with independent hackers, 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 on Friday, someone using a Lizard Squad Twitter account claimed the group was shifting its attention to attack a widely used Internet encryption service called Tor. Late in the day, a Tor spokeswoman said the service was responding to an attack but did not expect any "performance effects."