Sony did not respond to a request for comment on Tuesday. But the news site The Next Web reported that all Sony employees at the Los Angeles unit were ordered home and to stay off the company network.
A source within Sony told the news site that "a single server was compromised and the attack was spread from there."
An image posted on the Reddit social network from an individual claiming to be a former Sony employee showed a page with the words "Hacked by #GOP." It was unclear what GOP stands for, but some reports said the hacker group is called Guardians of Peace.
The posted image said unspecified demands must be met by Sony or important files would be released.
The website Geek.com said the hackers leaked a large file containing with spreadsheets and what appear to be passwords.
"We've already warned you, and this is just a beginning," the message posted on Reddit said.
"We continue till our request be met... If you don't obey us, we'll release the data shown to the world."
The Sony Pictures website appeared to be functioning normally Tuesday.
The Hollywood Reporter said it had confirmed the breach, but said the aims of the hackers were unclear.
A Sony statement to the entertainment publication said: "Sony Pictures Entertainment experienced a system disruption, which we are working diligently to resolve."