The Federal Bureau of Investigation officially said the North Korean government was behind the massive hack of sensitive and embarrassing information against Sony, a rare instance where the U.S. government is blaming a specific country for a cyberattack.
Here is the evidence the FBI said backs up its assessment:
* Technical analysis of the data deletion malware used in this attack revealed links to other malware that the FBI knows North Korean actors previously developed. For example, there were similarities in specific lines of code, encryption algorithms, data deletion methods, and compromised networks.
* The FBI also observed significant overlap between the infrastructure used in this attack and other malicious cyber activity the U.S. government has previously linked directly to North Korea. For example, the FBI discovered that several internet protocol (IP) addresses associated with known North Korean infrastructure communicated with IP addresses that were hardcoded into the data deletion malware used in this attack.
* Separately, the tools used in the SPE attack have similarities to a cyberattack in March of last year against South Korean banks and media outlets, which was carried out by North Korea.
"North Korea's attack on [Sony] reaffirms that cyber threats pose one of the gravest national security dangers to the United States," the agency said in a statement. "The destructive nature of this attack, coupled with its coercive nature, sets it apart. 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 agency said, adding that Sony reported the breach within hours.
The unprecedented hack made public a massive amount of sensitive and embarrassing data from the company, actors, and others in the entertainment industry. It also carried a threat from the hackers, who called themselves Guardians of Peace, threatening violence at theaters that showed the film, which depicts the fictional assassination of North Korea's leader, Kim Jong-un. Sony since scrapped the film's release, a decision that actors and politicians have criticized.
Homeland Security Secretary Jeh Johnson called the hack "an attack on our freedom of expression and way of life."
Sony executives also reportedly received an email on Thursday evening from the hackers, saying the company was "very wise" for canceing the worldwide release of The Interview, CNN reported.
The email received by Sony officials mimicked previous messages from the hackers, CNN reported:
The hacker message is effectively a victory lap, telling the studio, "Now we want you never let the movie released, distributed or leaked in any form of, for instance, DVD or piracy."
The message also says, "And we want everything related to the movie, including its trailers, as well as its full version down from any website hosting them immediately."
This is a breaking news story, please check back here and at BuzzFeed News on Twitter for updates.
Tom Namako is the deputy news director for BuzzFeed News and is based in New York.
Contact Tom Namako at firstname.lastname@example.org.
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