The PlayStation Network and Sony Entertainment Network, which are used by gamers to purchase and download titles and play games online, were taken offline for several hours on Sunday. Both are now back online.
PlayStation owners were originally told via an onscreen message that the service was down for maintenance, but Sony later admitted that the site closure was because of a DDoS attack.
At the time, on its blog, Sony said: "Like other major networks around the world, the PlayStation Network and Sony Entertainment Network have been impacted by an attempt to overwhelm our network with artificially high traffic.
"Although this has impacted your ability to access our network and enjoy our services, no personal information has been accessed."
In a more recent blog post, Sony said: "The networks were taken offline due to a distributed denial of service attack. We have seen no evidence of any intrusion to the network and no evidence of any unauthorised access to users’ personal information."
Responsibility for the attack has been claimed by hacker group Lizard Squad, which was also involved in a bomb threat to American Airlines on Sunday, when it tweeted: "@AmericanAir We have been receiving reports that @j_smedley's plane #362 from DFW to SAN has explosives on-board, please look into this."
The tweet referred to Sony Entertainment Online president John Smedley, who was on board the flight. The threat resulted in the flight to San Diego being diverted to Phoenix.
Other hacking groups have also claimed credit for the Sony attack.