Users are flooding the Internet Crime Complaint Center (IC3) with reports their machines are infected with the Reveton scareware.
The centre issued an alert warning of the malware which disguises itself by displaying a message to recipients that appears to come from the FBI.
Specifically, victims are told authorities have determined found their IP address to have visited child pornography sites.
Victims are lured to a website where Reveton is installed on their computer.
This causes their machine to freeze and a screen to display that carries a fake warning saying they have violated federal law.
The malware then attempts to extort money from the victim by ordering them to pay a fine in order to unlock their computer.
But even if victims pay the ransom, Reveton will remain on their machine and be capable of committing further fraud.
Reveton could also be part of a “malware cocktail," in which it is packaged with other malware, such as banking trojan Citadel.
Dell SecureWorks' Counter Threat Unit research technical director Jason Milletary said he suspects IC3 -- a project of the FBI and US White Collar Crime Unit -- is fielding a surge of complaints because of the malware's supposed connection to the FBI.
“The most important thing is not to give them any money, and don't try to contact the individuals,” Milletary said.
Usually, detection effectiveness will increase within days of malware being released, he added, though criminals are constantly tweaking virus' code so that it evades being flagged by anti-virus programs.
“It can be tricky because it tends to take over the machine,” Milletary said.
"You may also need to get onto another computer to find the instructions to get the virus off. If that fails, go the safe route and call a professional."
The FBI became aware of Reveton last year, and IC3 previously warned about it in May.