Firefox users may want to take note of a bug that is being actively exploited by attackers.

The attack takes place when users visit a “tech support” website which – as you may be able to guess – is simply a front that activates the bug in Firefox.

Upon the website loading the browser is frozen and a pop-up is displayed. The pop-up reads:

“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.”

The pop-up cannot be closed and the browser cannot be closed aside from forcing it to stop in Windows task manager or using the Force Close function in macOS.

Opening the browser again will open the web-page and users will need to close the tab before it is able to load again.

According to comments on Ars Technica, users can also disconnect their internet connection shortly after opening Firefox (with this bug being exploited) and closing the page to stop it before it loads.

The bug report issued by Malwarebytes’ head of threat intelligence Jérôme Segura outlines how attackers exploit the bug. The good news is there doesn’t appear to be any permanent damage.

With that having been said, Firefox is currently working on a fix and it’s a good idea to avoid clicking dodgy links.

A final word of advice – should you encounter this dodgy website do not call the telephone number displayed.

Brendyn Lotz writes news, reviews, and opinion pieces for Hypertext. His interests include SMEs, innovation on the African continent, cybersecurity, blockchain, games, geek culture and YouTube.