A number of employees at Sony Pictures Entertainment on Friday received emails that appear to be from the cyberterrorists who previously hacked into the company’s IT infrastructure and compromised sensitive information on film budgets, executive salaries and other information. In response, the FBI has launched an investigation.

Written in broken English, the emails from the alleged hacker group GOP – which stands for Guardians of Peace – indicated they would continue to attack Sony until the company collapsed. They provided no cause or specific demand. The group’s first attack occurred on Nov. 24, when Sony employees attempting to log into their network saw a screen with a picture of a skeleton and the words “Hacked by #GOP.”

While a theory has floated that the North Korean government may be behind the hacking in retaliation for the upcoming Sony film “The Interview” in which Seth Rogen and James Franco play conspirators to assassinate Kim Jong-Un, Pyongang says otherwise. Variety reported that a North Korean diplomat told Voice of America that “linking the DPRK to the Sony hacking is another fabrication targeting the country … My country publicly declared that it would follow international norms banning hacking and piracy.”

Variety posted the full email sent to Sony employees, which in part read: “Nothing can prevent us, but the only way is to follow our demand. Please sign your name to object the false of the company at the email address below if you don’t want to suffer damage. If you don’t, not only you but your family will be in danger.”

According to NBC News, the FBI said it was investigating the source of the emails. “Recent events underscore the persistence and maliciousness of harmful cyber criminals, and the FBI will continue to identify and apprehend those who pose a threat in cyberspace,” the FBI statement said.