Fraudsters are actively exploiting a bug in Firefox that causes the browser to freeze with a warning message the victim computer is running a pirated version of Windows.
As reported by ARS Technica, the scammers post the following message after a victim visits a malicious or compromised site (screenshot below):
“Please stop and do not close the PC… The registry key of your computer is locked. Why did we block your computer? The Windows registry key is illegal. The Windows desktop is using pirated software. The Window desktop sends viruses over the Internet. This Windows desktop is hacked. We block this computer for your safety.”
Furthermore, users are then warned to contact technical support via toll free number or risk the computer becoming disabled.
A security researcher Jérôme Segura confirmed several sites are exploiting the Firefox bug and subsequently reported the issue to Mozilla. The attack also works on Firefox versions running on Windows and Mac.
In addition, Mozilla is aware of the issue and actively working on a fix.
In the mean time, users can disconnect their computer from the internet, close the browser tab and then re-launch Firefox to help prevent connection to the offending site. Users should also never call the displayed phone number nor enter any sensitive information into pop-up windows generated by the scammers.