The hackers behind an “unparalleled” cyberattack on Sony Pictures Entertainment intended to both destroy property and leak sensitive information, a forensic investigator wrote in an email to Sony Corp. CEO Michael Lynton. The email did not include details on the hackers’ identities or the full extent of the damage to the company, Reuters reported Saturday.

"The scope of this attack differs from any we have responded to in the past, as its purpose was to both destroy property and release confidential information to the public,” wrote Kevin Mandia, an executive at FireEye Inc.’s Mandiant forensics unit. "The bottom line is that this was an unparalleled and well planned crime, carried out by an organized group, for which neither SPE nor other companies could have been fully prepared.”

The cyberattack that leaked confidential documents and unreleased movies in November also forced Sony to shut down its computer servers. It is considered one of the most extensive cyberattacks ever against a company in the United States. Among the leaked documents was data on the salaries of more than 6,000 Sony employees, including senior executives.

FBI spokesperson Joshua Campbell concurred with Mandiant’s findings, but declined to discuss details of the ongoing investigation. "The targeting of private-sector computer networks remains a significant threat, and the FBI will continue to identify, pursue, and defeat those who pose a threat in cyberspace," he said.

North Korea has emerged as a possible suspect in the breach, as the hackers used the same code that brought down South Korean ATMs and websites in 2013. Some have speculated North Korea could have targeted Sony because of its sponsorship of “The Interview,” a movie that spoofs the country and its leader, Kim Jong Un. North Korean officials have denied responsibility for the cyberattack.

Experts said it’s unlikely the cyberattack was a state-sponsored effort. Guardians of Peace, the group that claimed responsibility for the Sony hack, denied its actions were undertaken on behalf of a government.

The group accused Sony and Sony Pictures of "racial discrimination and human rights" violations in an email obtained by PC World. The email said numerous people were harmed by Sony's actions.