The FBI said Monday that it is working with other U.S. law enforcement agencies to investigate a hacking attack that hit Sony Pictures Entertainment last week, an incident that was possibly perpetrated by a group affiliated with North Korea.

“The FBI is working with our interagency partners to investigate the recently reported cyber-intrusion at Sony Pictures Entertainment,” the bureau said in an emailed statement. “The targeting of public and private sector computer networks remains a significant threat, and the FBI will continue to identify, pursue and defeat individuals and groups who pose a threat in cyberspace.”

By Monday, SPE had made progress recovering from the Nov. 24 attack, which had effectively disabled its email and other internal systems. Certain critical business systems are now back online, with email service also expected to return on Monday, Variety reported.

The hack resulted in five Sony films — including “Fury” (starring Brad Pitt, pictured above) and unreleased movies such as “Annie” and “Mr. Turner” — being stolen and posted to piracy networks. Sony is working with the FBI and other agencies to investigate the breach, and the studio has hired security firm FireEye and its Mandiant unit to look into the incident.

In the hack, an image of a skeleton appeared on company computers with a message that said, “Hacked by #GOP,” with the group behind it calling itself “Guardians of Peace.” The message threatened to release “secrets and top secrets” of the company.

Sony has been looking into the possibility that hackers with ties to the North Korean regime were behind the assault, although it had not turned up direct evidence of that. The studio has set a Dec. 25 release for “The Interview,” a geopolitical spoof starring James Franco and Seth Rogen, in which the duo are approached by the CIA about assassinating North Korean dictator Kim Jong-un.

The hackers who took down Sony Pictures used tools “very similar” to those used last year in cyberattacks on South Korean TV stations and ATMs, which the South Korean government blamed on North Korea, the Wall Street Journal reported, citing anonymous sources.

In a statement, an SPE company rep said: “Sony Pictures continues to work through issues related to what was clearly a cyber attack last week. The company has restored a number of important services to ensure ongoing business continuity and is working closely with law enforcement officials to investigate the matter.”