FBI is confident North Korea is behind 'the most serious cyberattack' made against US

The FBI has "very high confidence" that North Korea hacked Sony, resulting in "the most serious cyberattack ever made against US interests," The Verge reports.

FBI director James Comey and director of national intelligence James Clapper spoke at a cybersecurity conference in New York today. Clapper weighed in on the severity of the attack during the conference earlier this morning. Later, Comey was able to provide more details about the hack.

"We know who hacked Sony," Comey said. "It was the North Koreans."

Comey said that the Guardians of Peace "got sloppy" in hiding their IP addresses. With this information, FBI security researchers traced internet activity to connections in North Korea. Because web access within the country is limited, a third party using a North Korean IP without permission from the government would be unlikely.

In November 2014, the attack on Sony Pictures' computer systems resulted in a massive leak of personal and company data. The hack is associated with the then-impending release of the Seth Rogen film The Interview; it was followed with threats invoking the 9/11 attack, causing major U.S. theater chains to postpone the film and Sony to pull it from theaters before deciding to release it online. Since its release, the movie has raked in more than $31 million online and $5 million from select theaters.

North Korea has denied any connections to the attack, though it has praised the Sony hack as a "righteous deed."

President Barack Obama previously stated that the U.S. will respond "proportionally and in a place and time we choose." The U.S. has since imposed sanctions against the country's arms industry, the Wall Street Journal reports, in order to "isolate key North Korean entities and disrupt the activities of close to a dozen critical North Korean operatives."