The cyberattack against Sony Pictures Entertainment in November was the “most serious” in histroy against a U.S. interest, the U.S. Director of National Intelligence said Wednesday.

Speaking at an online security conference held at New York City’s Fordham University, James Clapper’s comments were followed by a speech by FBI Director James Comey who revealed how the agency discovered that North Korea was behind the hack.

Comey said the hackers “got sloppy” and used Internet connections the FBI knew were exclusive to North Korea. 

"We know who hacked Sony. It was the North Koreans," Comey said, adding that since Web access is highly restricted in the repressive nation, it is extremely unlikely the hackers would be able to capture an official connection without government consent. 

Clapper said he has seen “The Interview,” the comedy that depicts the assassination of North Korean dictator Kim Jong-Un and the hackers’ stated motivation for the attack.

“It’s obvious to me the North Koreans don’t have a sense of humor,” he told the auidence.

The North Korean government called the film an act of war.

"They are deadly serious about affronts to the Supreme Leader," Clapper said of the North Koreans. "They will keep doing it again and again until we push back."

Clapper, who recently visited the isolated nation to negotiate the release of two American hostages, advocated for the U.S. to retaliate to the attack during his address.

"We have to push back,” Clapper said. "If they get global recognition with no consequence they’ll do it again and again.”

The attack led Sony to perform several about-faces regarding the release of “The Interview,” which has to date grossed $31 million in online and cable salesr, as well as $5 million at traditional movie theaters. 

Anadolu Agency