The head of the FBI said Wednesday that the shadowy hacker group blamed by the U.S. for the computer attack against Sony Pictures Entertainment "got sloppy" and left behind clues that point to North Korea's involvement.
FBI Director James Comey also pushed back hard against suggestions that the bureau was wrong in identifying North Korea as the source of last fall's cyberattack.
"I know that some serious folks have suggested that we have it wrong," Comey said at a speech at Fordham University. "They don't have the facts that I have. They don't see what I see."
Comey said that Guardians of Peace, the group that claimed responsibility for the hack, had previously sent threatening emails to Sony, sometimes using an Internet provider address used exclusively by North Korea.
"It was a mistake by them that we haven't told you about before that was a very clear indication of who was doing this," Comey said. "They would shut it off very quickly once they realized the mistake, but not before we saw them and knew where it was coming from."
"I remain where I started: with not just high confidence but very high confidence about who perpetrated this attack," Comey said.
Comey appeared to be responding to cybersecurity experts who told the Los Angeles Times and others that they were unconvinced that North Korea was involved. Instead, many thought a disgruntled former employee was the likely culprit.
The hack, which became public Nov. 24, appeared to be in retaliation for Sony's planned release of "The Interview," a satirical comedy about North Korean leader Kim Jong Un, which depicts a fictional assassination attempt on Kim.
Sony at first decided to cancel its release of the film after Guardians of Peace threatened to attack movie theaters showing it, but later released it to a small number of theaters and online over the Christmas holiday.
Director of National Intelligence James Clapper, speaking at the same conference at Fordham, said the North Korean military's Reconnaissance General Bureau was responsible for "overseeing" the attack against Sony.
Clapper said he had a tense dinner with the head of the Reconnaissance General Bureau, Gen. Kim Youn Chol, when he traveled to North Korea last year to retrieve two American prisoners.
"Cyber is a powerful new realm for them where they believe they can exert maximum influence at minimum cost," Clapper said. "This episode with Sony has shown that they can get recognition for their cyber capabilities and that is why we have to push back," he said.
"I watched 'The Interview' over the weekend, and it is obvious to me that the North Koreans don't have a sense of humor," he said.