Hackers invoked the 9/11 attacks Tuesday in their most chilling threat yet against Sony Pictures, again warning the Hollywood studio not to release a film which has angered North Korea.

The threat came as lawyers filed a class action suit against the embattled studio alleging that it failed to protect employees' data, stolen in a massive cyber-attack three weeks ago.

In a new statement cited by US media, the GOP (Guardians of Peace) hacking group announced the start of a threatened "Christmas gift," including leaked emails from Sony boss Michael Lynton.

Specifically, it warned movie-goers against seeing "The Interview," the Sony comedy starring James Franco and Seth Rogen about a fictional CIA plot to assassinate North Korean leader Kim Jong-Un.

"We will clearly show it to you at the very time and places 'The Interview' be shown, including the premiere, how bitter fate those who seek fun in terror should be doomed to," it said, in broken English as previously.

"Soon all the world will see what an awful movie Sony Pictures Entertainment has made. The world will be full of fear," added the statement, cited by the Los Angeles Times and The Wrap among others.

And it warned: "Remember the 11th of September 2001. We recommend you to keep yourself distant from the places at that time. (If your house is nearby, you'd better leave.)

"Whatever comes in the coming days is called by the greed of Sony Pictures Entertainment. All the world will denounce the SONY."

- Lawsuit targets Sony -

The threat came a day after Sony Pictures boss Lynton sought to reassure employees at a staff meeting, vowing the studio will not be destroyed by the leaks, a day after hackers promised a big "Christmas gift."

"This will not take us down," Lynton told employees, adding: "You should not be worried about the future of this studio."

The hackers have demanded that Sony stop the release due on December 25 -- Christmas Day -- of the comedy "The Interview."

The movie was originally due out in October. Speculation has grown that its release could be delayed again, although Sony has made no comment or suggestion that it could give in to the hackers' demands.

North Korea has denied involvement in the brazen November 24 cyber-attack, but praised it as a "righteous deed" potentially orchestrated by supporters furious over the movie.

Meanwhile, lawyers said Tuesday they have filed a class action suit against Sony Pictures.

The lawsuit, filed in Los Angeles, alleges that "Sony failed to secure and protect its computer systems, servers, and databases, resulting in the release of the named plaintiffs and other class members'" personal data.

"An epic nightmare, much better suited to a cinematic thriller than to real life, is unfolding in slow motion for Sony's current and former employees," said the 45-page lawsuit.

"Their most sensitive data, including over 47,000 Social Security numbers, employment files including salaries, medical information, and anything else that their employer Sony touched, has been leaked to the public, and may even be in the hands of criminals," it said.

The lawsuit was filed Monday by two former Sony employees, on behalf of others in a similar situation, said Seattle-based lawyers Keller-Rohrback, who provided AFP with a copy of the suit.

"Because of Sony's failure to protect its current and former employees' private information, that information is now circulating online, putting those employees at risk," it said.