Sloppiness or forgetfulness on the part of the hackers who targeted Sony Pictures Entertainment over "The Interview" helped the FBI trace the attack to North Korea, CNET reported.

Although they used used proxy servers in an attempt to disguise their identity, the intruders "got sloppy" several times, according to James Comey, the bureau's director.

"Either because they forgot or because of a technical problem, they connected directly, and we could see that the IPs they were using ... were exclusively used by the North Koreans," James Comey said on Wednesday at an event at New York's Fordham University.

In each case, the hackers rapidly noted the error they were committing, the FBI chief said.

"They shut it off very quickly once they saw the mistake -- but not before we saw where it was coming from," Comey explained.

The director said that the FBI has "very high confidence" that Pyongyang is to blame for the attack on the movie house, Wired reported. The hackers, who referred to themselves as "Guardians of Peace," claimed to have stolen more than 100 terabytes of Sony Pictures data.

The attack seems to have been in response to the release of Sony's "The Interview," a comedy that portrays North Korean dictator Kim Jong-Un in a negative light. Through diplomats in New York, the hermit kingdom's government denied involvement in the incident, though it also qualified the hackers' motives as "righteous."

Beyond the technical evidence, Comey said that a "behavioral analysis unit" of FBI experts trained to psychologically analyze enemies based on their writings and actions supported suspicions directed at North Korea.

The Obama administration has publicly accused Pyongyang in the hack, and additional sanctions have been placed on North Korea as a result. Its regime's "provocative, destabilizing and repressive actions and policies ... including its destructive, coercive cyber-related actions during November and December 2014" necessitated that step, President Obama has said.

Director of National Intelligence James Clapper, who also spoke at Fordham, meanwhile accused the North Korean leadership of lacking a sense of humor.

"They really do believe they are under siege from all directions," Clapper noted.

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