North Korea was responsible for a "destructive" cyber attack on Sony Pictures, the US Federal Bureau of Investigation has said, warning it will hunt down the perpetrators and make them pay.

"Such acts of intimidation fall outside the bounds of acceptable state behaviour," the FBI said in a statement on Friday, adding it would "identify, pursue, and impose costs and consequences on individuals, groups, or nation states who use cyber means to threaten the United States or US interests."

The FBI's case cited, among other factors, technical similarities between the Sony break-in and past "malicious cyber activity" linked directly to North Korea.

The FBI based its conclusion on the following points:

  • Malware used in the attack linked to previous cyber attacks that originated in North Korea.
  • The FBI also observed significant overlap between the infrastructure used in this attack and other past malicious cyber activity.
  • Separately, the tools used in the latest attack have similarities to a cyber attack in March of last year against South Korean banks and media outlets

Barack Obama administration officials had previously declined to openly blame North Korea but said they were weighing various options for a response. The statement on Friday did not reveal what options were being considered.

The break-in escalated to terrorist threats that promoted Sony to cancel the Christmas release of the movie "The Interview". The comedy is about a plot to assassinate North Korea's leader, Kim Jong-Un.

Hackers have sent a new email to Sony Pictures, praising the studio as "very wise" to cancel the release of the movie and saying Sony's data is safe "as long as you make no more trouble".

The message warned to "never" release the film "in any form", including on DVD, AP news agency reported.

But when Al Jazeera contacted Sony's press office, they refused to confirm or comment on in terms of the new threat.

President Obama said on Friday that Sony made a mistake in pulling the film from theatres.

"Sony as a corporation suffered significant damage. I am sympathetic to the concerns they have faced. Yes, having said that I think they made a mistake. We cannot have a society in which some dictators decide to impose censorship in the US," he said.

Source: Al Jazeera and agencies