The Federal Bureau of Investigation says that North Korea is behind the cyberattack on Sony last month that's led to the release of stolen emails and social security numbers and the cancellation of The Interview. The FBI formally identified North Korea's government as culprit in the hack this morning, following anonymous reports from US officials Wednesday evening. North Korea has been widely suspected to be behind these attacks for weeks.

"Such actions of intimidation fall outside the bounds of acceptable state behavior."

"We are deeply concerned about the destructive nature of this attack on a private sector entity and the ordinary citizens who worked there," the bureau writes, saying that this hack emphasizes why cyberattacks are among the biggest national security threats. "North Korea's actions were intended to inflict significant harm on a US business and suppress the right of American citizens to express themselves. Such actions of intimidation fall outside the bounds of acceptable state behavior."

The FBI does not say what actions it will be taking in response to this attack. President Obama is expected to speak this afternoon, when he will likely explain how the US will respond to North Korea. The White House began setting expectations for his response yesterday, explaining that the response must be "proportional," as the attackers may be looking to elicit a certain reaction.

The bureau says that the malware used to attack Sony is related to malware that has previously been used by North Korea. "For example, there were similarities in specific lines of code, encryption algorithms, data deletion methods, and compromised networks," the bureau writes. It also saw "significant overlap" in the infrastructure used in this attack and the infrastructure used in past attacks linked to North Korea. Similar tools were used as well.

Many of these similarities have been reported in the press over the past few weeks, making these conclusions largely unsurprising. However, the FBI also notes that it used "sensitive sources and methods" in identifying the party behind this attack, and those sources and methods are not being described.

Sony first became aware of the attack in late November, when its computer systems were brought down globally. A group calling itself the "Guardians of Peace" took responsibility for the attack, and since last week it's been releasing stolen Sony files online. On Tuesday, the hackers also threatened attacks on screenings of the film The Interview, leading Sony to cancel its release.

North Korea is presumed to take issue with the content of The Interview, which is about an assassination attempt on its leader, Kim Jong-un, and depicts him dying graphically. The comedy stars Seth Rogen and James Franco and was planned for a Christmas Day release. That will no longer happen. In fact, Sony has insinuated that it may choose not to release The Interview at all, including online, on-demand, or on DVD and Blu-ray. That would amount to a big loss for Sony: The Wrap reports it's already spent around $90 million on the film, and that Sony expected to take in at least $210 million in return.

The FBI's full statement is reprinted below: