There is enough information to conclude that the North Korean government is responsible for the Sony cyberattack, the FBI said Friday, based on an investigation conducted in collaboration with other government agencies and departments.
"Though the FBI has seen a wide variety and increasing number of cyber intrusions, the destructive nature of this attack, coupled with its coercive nature, sets it apart," the agency said in a statement. "North Korea's actions were intended to inflict significant harm on a U.S. business and suppress the right of American citizens to express themselves. Such acts of intimidation fall outside the bounds of acceptable state behavior."
The U.S. is considering options for a 'proportional' response to the cyberattack. One option is to place North Korea back on the terror list as a state sponsor of terror, Dow Jones reported Friday.
The U.S. is also consulting several countries on the cyberattack, including Japan, South Korea, China and Russia, according to a U.S. official, who added that the U.S. is "working through diplomatic channels to register our concerns and ask for assistance."
Due to sensitive sources and methods to obtain the information, the FBI said it is limited in what it can share. The bureau did say that the conclusion is based on technical analysis of data deletion malware, which revealed that there were links to other malware that North Koreans previously developed. The agency also noticed significant overlap between the infrastructure used in the Sony attack and other malicious digital activity from North Korea.
Shares of Sony were down nearly 3 percent.
The Chinese government, responding to a U.S. official's allegation that there may be Chinese involvement in the hack, said it does not support illegal cyber action within its borders and urged the U.S. to share evidence, according to representatives of the Chinese embassy in Washington.
Former Sen. Chris Dodd, CEO of the Motion Picture Association of America, called the North Korean attack a "despicable, criminal act."
"This situation is larger than a movie's release or the contents of someone's private emails. This is about the fact that criminals were able to hack in and steal what has now been identified as many times the volume of all of the printed material in the Library of Congress and threaten the livelihoods of thousands of Americans who work in the film and television industry, as well as the millions who simply choose to go to the movies," Dodd said. He added that this cannot be allowed to happen again to American corporations.
According to a source close to the studio, the hackers emailed a message to Sony executives approving the studio's decision to postpone the release of the movie "The Interview," a comedy about an attempted assassination of North Korea's leader, Kim Jong Un. The authenticity of the message has yet to be verified.
The hackers had new commands for Sony: "Now we want you never let the movie released, distributed or leaked in any form of, for instance, DVD or piracy," the email said. "And we want everything related to the movie, including its trailers, as well as its full version down from any website hosting them immediately."
The hackers reminded executives that they "still have your private and sensitive data," which they said will remain secure "unless you make additional trouble."
In late November, Sony confirmed that the cyberattack destroyed systems and stole large quantities of personal and commercial data. A group calling itself "Guardians of Peace" claimed responsibility and issued threats against Sony. The attacks rendered thousands of Sony computers inoperable and forced the company to take its computer network off line.
—With reporting by CNBC's Julia Boorstin. Reuters contributed to this report.