The director of the FBI said Wednesday the agency is confident in its assertion that North Korea was responsible for a hack of Sony Pictures Entertainment.
James Comey acknowledged that some network security experts had suggested that the FBI got it wrong, but said those people “don’t have the facts that I have.”
Speaking at the International Conference on Cyber Security in New York, Comey said in light of the questions that had been raised the FBI decided to declassify some information.
The Guardians of Peace, which claimed responsibility for the cyberattack, sent emails threatening Sony employees and post various statements online using a proxy server to disguise where the messages and posts were coming from, he said.
But they “got sloppy” several times and forgot to use the proxy server, and investigators could then see that the IP addresses being used were “exclusively used by the North Koreans,” Comey said.
“It was a mistake by them. 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,” he said. He called it a “very clear indication” that North Korea was behind the attack.
The FBI hadn’t previously disclosed the information because it wanted to protect its detection methods.
The hack against Sony Pictures caused an uproar that prompted the studio to cancel the planned release of its film The Interview in about 8,000 mainstream cinemas. Some of the threats against Sony Pictures indicated movie audiences could be targeted.
Sony Pictures decided to release the movie in independent cinemas in the US and online. It said Tuesday it had taken in 36 million dollars in revenue from cinema, online and video on demand sales in the first 10 days. The film cost an estimated 44 million dollars to make.
The fictional film angered North Korea because it depicts the assassination of North Korean leader Kim Jong Un.
The US announced new sanctions against North Korea in retaliation for the hack last week.