Sony said its PlayStation Network was back online on Monday following a cyber attack that took it down over the weekend.<br /><br />It was a so-called denial of service attack, whereby the system was overloaded by vast amounts of malicious traffic.<br /><br />The network itself, and registered information of its 53 million users, was not accessed. <br /><br />The people who claimed they were behind the attack said it was intended to pressure Sony to spend more of its profits on the network.<br /><br />A Twitter user with the handle @LizardSquad send the message: “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.”<br /><br />The same group was also believed to be behind a bomb scare on a commercial airline flight carrying Sony Online Entertainment President John Smedley.<br /><br />A PlayStation spokeswoman in the United States said the FBI was investigating the diversion of the Dallas/Fort Worth to San Diego flight. <br /><br />Lizard Squad said it had also targeted the servers of World of Warcraft video gamemakers Blizzard Entertainment, whose website was down for a while at the weekend. <br /><br />It threatened to attack Microsoft’s Xbox Live network and some users said they had problems accessing it on Sunday.