Was Sony hack in retaliation for upcoming movie?

The FBI is investigating the destructive cyber-attack at Sony Pictures, and also warning that other companies could be next.

Sources say the cyber-attack on Sony Picures used an especially aggressive malware capable of erasing hard drives and crashing computer networks.

Hackers, calling themselves "The Guardians of Peace," stole the personal information of more than 6,000 Sony employees, and four unreleased Sony films were posted to the Internet.

Now investigators are wondering if the attack might be retaliation for another upcoming Sony movie "The Interview," a comedy in which TV reporters are recruited to assassinate North Korean leader Kim Jong-un.

Investigators wonder if the plot of that movie may have triggered retaliation against Sony. Sources say the malware code is written in Korean, and North Korean hackers have used a similar cyber weapon before in a 2013 attack on banks and broadcasters in South Korea.

Cyber analyst James Lewis says the use of malicious software that can destroy data is an escalation on the cyber front.

"This signals a new capability for North Korea," he said. "Most of the breaches are smash and grab. So, if the North Koreans did indeed erase data, that's a step up. That's more like an attack than what we've seen in the past."

Lewis says that kind of damage can be permanent if companies, like Sony, don't routinely back up sensitive files.

"My lesson is, you know, if you're going to make fun of the Dear Leader, maybe you should think twice if you don't have backups."

The FBI has not publicly identified North Korea as a suspect. But, federal investigators are sharing information about the malware with other companies and urging them to tighten cyber defenses.