The company said that it had taken the PSN down voluntarily while it investigated an "external intrusion".
The system is still unavailable five days after the hack was discovered.
Users trying to connect have been met with error messages stating that the network is "undergoing maintenance" or is "suspended".
The PlayStation Network is used by owners of PS3 and PlayStation Portable machines to download games, films and music, as well as to play online with friends.
According to Sony, it has more than 70m accounts registered worldwide. the company thanked users for their patience and assured them that it was working "around the clock" to strengthen the network infrastructure.
"Though this task is time-consuming, we decided it was worth the time necessary to provide the system with additional security," wrote Patrick Seybold, the company's senior director of corporate communications and social media.
The statement did not address the issue of personal information, including credit card details, stored by PSN.
Anonymous denial 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."
'Really not good' As well as gaming, the outage has affected other services running over the PlayStation Network.
UK-based film rental site LoveFilm confirmed to the BBC that its customers are currently unable to stream films on the service. In the US, some users of Netflix - another movie streaming service - have also reported problems.
This outage is the latest in a series of problems for the network which has suffered extended periods of downtime over the past few weeks.
Angry gamers have flooded blogs, forums and Twitter with complaints.
"It wouldn't be as bad if we got an ETA of when it will be back up and running but instead we are greeted with one update on the situation a day all saying it will be back up soon," wrote one user, geddesmond2.
Others, however, were more accommodating. "Keep up the good work Sony... take your time," wrote deltaman-3.
'Poor timing' Oli Welsh, from Eurogamer.net, said that the outage was a big problem for Sony - especially at Easter.
"As much as the weather's lovely, a lot of gamers will be looking forward to tucking in to their favourite hobby this week.
"It's also a pretty big week for new releases, the biggest we've had in a couple of months. There's one really key game coming out called Portal 2 which has a great online mode that a lot of people now won't be able to access straight away.
"For gamers it's a shame, and for Sony it's a problem."
He added that customers may expect some kind of reimbursement for the downtime.