Sony Pictures denounced Wednesday a "brazen" cyberattack it said netted a "large amount" of confidential information, including movies as well as personnel and business files.

But the entertainment giant downplayed a report that North Korea was behind the attack, saying it did not yet know the full extent of the "malicious" security breach.

"The investigation continues into this very sophisticated cyberattack," a Sony Pictures Entertainment spokeswoman told AFP, a day after the FBI confirmed it was probing the hack attack.

The company, which had not previously confirmed the breach, emailed a memo to staff late Tuesday updating them on the extent of the hack.

"It is now apparent that a large amount of confidential Sony Pictures Entertainment data has been stolen by the cyberattackers, including personnel information and business documents," it said.

"This is the result of a brazen attack on our company, our employees and our business partners. This theft of Sony materials and the release of employee and other information are malicious criminal acts," the memo added.

According to The Washington Post, the hackers used malware similar to that used to launch destructive attacks on businesses in South Korea and the Middle East, including one against oil producer Saudi Aramco.

Some reports said Sony is looking into whether North Korea may have been behind the major cyberattack on the studio last week, possibly over an upcoming comedy film about a CIA plot to assassinate its leader Kim Jong-Un.

"The Interview," which stars Seth Rogen and James Franco as two journalists recruited by the CIA to bump off Kim, has infuriated the North Koreans, with state media warning of "merciless retaliation."

The website re/code reported that Sony Pictures was set to officially name North Korea as the source of the hacking attack, saying an announcement could come within the day.

But the Sony Pictures spokeswoman said the report was "not accurate," declining to give any further details.

She confirmed to AFP the authenticity of the staff memo, published by the entertainment news site Variety.

Variety has reported that unreleased Sony movies, including the upcoming "Annie," have been made available on illegal file-sharing websites.

The war film "Fury," as well as "Mr Turner," "Still Alice" and "To Write Love on Her Arms" were also made available.