In a blog post, Sony said both the PlayStation Network and Sony Entertainment Network are now back online.
The post 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."
Explaining what had happened, the entertainment technology giant 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."
Sony said that in light of the issue the networks will not undergo the scheduled maintenance which was planned for today.
The blog post added: "We will provide an update shortly for when the maintenance will be rescheduled.
"We sincerely apologise for the inconvenience caused by this issue. Thanks for your patience and support."