LOS ANGELES (CBS/AP) — The FBI said Friday it is investigating threatening emails sent to some employees of Sony Pictures Entertainment, which was hit by a cyberattack last week that disrupted its computer system and spewed confidential information onto the Internet.
The FBI was trying to identify the person or group responsible, the agency said in a statement. It did not provide any details.
However, the trade paper Variety said the email written in broken English claimed to be from the head of the GOP — short for Guardians of Peace — the same group that took credit for last week's attack.
"Removing Sony Pictures on earth is a very tiny work for our group which is a worldwide organization. And what we have done so far is only a small part of our further plan," the email read.
Later, the email warns employees: "Please sign your name to object the false of the company at the email address below if you don't want to suffer damage. If you don't, not only you but your family will be in danger."
"Make your company behave wisely," the email urges.
The Los Angeles Times reported the email was received Friday.
A Sony spokesman confirmed in an email to the Times that "some of our employees have received an email claiming to be from GOP" and said the company was working with law enforcement.
Employees were told to turn off their mobile devices after receiving the message, Variety said, citing Sony insiders it did not name.
Messages from The Associated Press to Sony representatives were not immediate returned.
Recently, hackers released personal information for thousands of Sony employees online, including some Social Security numbers and the purported salaries of top executives. Five movies, including the unreleased "Annie," also have shown up on file-sharing websites.
On Nov. 24, workers who logged onto Sony Pictures' network saw a skeleton and the message "Hacked by #GOP."
There has been speculation that North Korea was behind the attacks in retaliation for the upcoming movie "The Interview," a comedy starring Seth Rogen and James Franco that depicts an assassination attempt on that country's leader, Kim Jong Un.
North Korea denied involvement Thursday.
Some cybersecurity experts say they've found striking similarities between the code used in the hack of Sony Pictures Entertainment and attacks blamed on North Korea that targeted South Korean companies and government agencies last year.
Experts are divided, however, over the likelihood that North Korea or independent hackers were involved.
Another group, God'sApstls, was found on the malware software used to break into Sony's computers and steal data before erasing sensitive documents from the hard drives.
Professor Clifford Neuman, director of USC's Center for Computer Systems Security, pointed to an extortion element in the emails he finds worrisome.
"Someone may have obtained access to some of the machines and made for sale to others which then could have been leveraged by different groups: one targeting extortion, one targeting terrorist threats," he said. "I'm a little more concerned monetary motive here because it means other companies are at risk."
The FBI says it will hold cyber security briefings with Sony staff Wednesday.
(TM and © Copyright 2014 CBS Local Media, a division of CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2013 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)
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