Sony's PlayStation Network was back online on Monday following a cyber attack that took it down over the weekend, which coincided with a bomb scare on a U.S. commercial flight carrying a top Sony executive.
Sony said on its PlayStation blog that the network had been taken down by a denial-of-service-style attack, which overwhelmed the system with traffic but did not intrude into the network or access information of its 53 million users.
Meanwhile, the Federal Bureau of Investigation (FBI) said it was investigating the bomb threat that caused an American Airlines flight to be diverted.
A Twitter account with the handle zLizardSquad claimed responsibility for Sunday's attack and said it was meant to pressure Sony to invest more in the network.
"Sony, yet another large company, but they aren't spending the waves of cash they obtain on their customers' (PlayStation Network) service. End the greed,'' one post said.
Sony's was the victim of a notorious 2011 breach that compromised data of tens of millions of PlayStation Network users, dealing a major blow to plans for a looser network designed to allow for the connection of a range of Sony devices.
Since then it has invested heavily in securing the network, which it hopes can serve as a centerpiece of its plans to rebuild its business after years of losses in its flagship electronics operations.
Lizard Squad said it had also targeted servers of World of Warcraft video game maker Blizzard Entertainment, whose website was down. It threatened to attack Microsoft's Xbox Live network, which some users said they had problems accessing on Sunday.