An entrance gate to Sony Pictures Entertainment at the Sony Pictures lot is pictured in Culver City, California. The FBI is investigating the leak of unreleased movies, produced by Sony, after the company was targeted by a massive cyberattack last week. Reuters/Fred Prouser

Sony Pictures Entertainment has reportedly called in the FBI to investigate a massive cyberattack, which compromised the company’s computer networks last week. The breach was followed by the leak of at least five Sony-produced movies, including four unreleased ones, on pirate websites.

The unreleased movies produced by the company were leaked on file-sharing websites this weekend. Although the appearance of the pirated movies coincides with last week’s hack of Sony’s movie studio, a connection between the two incidents is yet to be established.

While the FBI is examining the illegal release of the movies on file-sharing websites, FireEye Inc's Mandiant forensics unit, which helps hacking victims identify the extent of attacks and restore systems, has also been hired to clean up the massive cyberattack, Reuters reported, citing three people familiar with the matter.

The leak of the Sony movies was first reported by Variety on Saturday, saying that “Fury,” a World War II drama starring Brad Pitt, was downloaded by more than 888,000 unique IP addresses since the movie showed up online on Thursday. By Sunday noon, the movie had been downloaded more than 1.2 million times.

According to piracy-tracking firm Excipio, “Annie” was downloaded 206,000 times, while downloads of the other movies -- “Still Alice,” “Mr. Turner” and “To Write Love on Her Arms” -- stood at 103,832, 63,379 and 19,946 times, respectively. All the movies except “To Write Love on Her Arms,” are scheduled for a December release.

Technology news website Re/code reported on Friday that Sony and outside security firms were investigating if the hackers that breached the company’s computer networks were backed by the North Korean government -- possibly operating out of China -- in retribution for the studio's support for “The Interview,” which is set to be released on Dec. 25 in the U.S. and Canada.

“The Interview” is a comedy about a CIA attempt to assassinate North Korean leader Kim Jong Un. The Pyongyang government has criticized Sony for producing the movie, denouncing it as “undisguised sponsoring of terrorism, as well as an act of war” in a letter to the United Nations.