FBI says North Korean government was responsible for the Sony cyber attack

The United States on Friday blamed North Korea for the devastating cyberattack against Sony Pictures, formally acknowledging the involvement of the Pyongyang government and saying the tools and infrastructure used in the attack were similar to previous activity from North Korea.

The "destructive nature" of the attack, which led the big Hollywood studio to pull a movie depicting North Korea's leader amid threats, coupled with "its coercive nature," set it apart from previous attacks, the FBI said.

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Here's how the agency put in in a press release:

"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 cyber attack in March of last year against South Korean banks and media outlets, which was carried out by North Korea."

On Friday afternoon, President Barack Obama said the United States would "respond proportionally" to the attack. He also called Sony's decision to pull "The Interview" a mistake. 

"We cannot have a society in which some dictator someplace can start imposing censorship in the United States," he added.

Reuters contributed to this report.