In recent weeks, Sony has been targeted by hackers' group Anonymous.
In a message posted on the AnonOps blog, it said "for once we didn't do it".
However, it suggested that some members may have acted on their own without the group's knowledge.
Anonymous has been critical of the Japan-based entertainment giant over its treatment of George Hotz, an American hacker who unlocked the PS3's closed operating system.
Sony filed a lawsuit against the 21-year-old, arguing that his hack had allowed pirated games to be played on the machine.
The case was dropped earlier this month after Mr Hotz agreed to an injunction banning him from similar behaviour in future.
In denying responsibility for the attack, Anonymous said: "A more likely explanation is that Sony is taking advantage of Anonymous' previous ill-will towards the company to distract users from the fact that the outage is actually an internal problem with the company's servers.