Films reviews often feature tough criticism, but they rarely do they promise "stern" and "merciless" retribution.

That was North Korea’s response to the upcoming Seth Rogen and James Franco comedy “The Interview,” about a CIA plot to assassinate Kim Jong Un. The isolated country also called the movie an “act of war.”

Now the FBI is investigating whether North Korea had anything to do with last week's cyberattack on Sony Pictures Entertainment, which is producing “The Interview.”

The company found that their internal corporate network had been hacked. Before its computer system went down, employees were sent a message displaying a red skeleton and the text "Hacked By #GOP." GOP reportedly stands for Guardians of Peace.

"We've obtained all of your internal data, including your secrets," the message said, also threatening to release sensitive data.

DVD screener copies of the Sony movies "Fury," "Still Alice," "Mr. Turner," "To Write Love on Her Arms" and "Annie" began popping up online, though there is no confirmation that these links came from the same breach.

With the exception of "Fury," the films had yet to be released.

According to a thread on Reddit, documents containing passport and visa information for cast and crew, email inboxes, IT systems documents, and accounting and research information may have been exposed.

Sony has condemned the attack, but has released few details.

“The theft of Sony Pictures Entertainment content is a criminal matter, and we are working closely with law enforcement to address it,” the studio said in a statement.

When asked about the attack, a spokesman for North Korea's UN mission said: "The hostile forces are relating everything to the DPRK (North Korea).

I kindly advise you to just wait and see"

North Korea often refers to the U.S. and South Korea as hostile forces.