Sony Corp worked for a third day on Saturday to restore services to its PlayStation network (PSN) as the FBI said it was looking into the disruption, which began on Christmas Day.
"We are aware of the reports and are investigating the Sony PlayStation matter," FBI spokeswoman Jenny Shearer said via e-mail. She did not elaborate.
Meanwhile Sony said on Saturday that the attack had prevented some people who received consoles for Christmas from using their new machines on the PlayStation network, which lets gamers compete with people around the world via the Internet.
"If you received a PlayStation console over the holidays and have been unable to log onto the network, know that this problem is temporary and is not caused by your game console," Sony executive Catherine Jensen said on the company's US PlayStation blog.
Later in the day she said the company had restored access for some users and would keep bringing more back online.
Sony, however, declined to say how many of PSN's 56 million users had been affected by the attack.
The blog said the problems were the result of "high levels of traffic designed to disrupt connectivity and online game play," which is widely known as a distributed denial-of-service attack.
A hacker activist group known as Lizard Squad said it was responsible for the PSN outage as well as delays on Microsoft's Corp's Xbox network.
Microsoft quickly fixed the problem.