The ransomware known as Reveton was first detected in May 2012, directing victims to a website that installed it on their computers.
Ransomware is used to intimidate victims into paying a fine to "unlock" their computers, but paying the fine does nothing to solve the problem with the computer.
The newest version of the ransomware is now targeting OS X Mac users, the FBI's Internet Crime Complaint Center said Thursday.
The ransomware is pushed to victims' computers when they browse common websites, and once the web browser is exploited, the victims' computer displays a pop-up warning that appears to be from the FBI.
The warning accuses victims of violating various U.S. laws and locks their computer. Victims are told that to unlock the computer and avoid legal issues they must pay a $300 fine via a prepaid money card.
Ransomware is considered an attempt to extort money, the FBI said, urging victims to disregard payment instructions and file a complaint at http://www.ic3.gov/.