Critical Firefox Update (firefox-patch.js) Virus Scam – How to Remove It

Critical Firefox Update (firefox-patch.js) Virus Scam – How to Remove It

This article has been created to explain what is the Critical Firefox Update virus and how to stop such malicious redirects to dangerous pages in the future.

A new redirect web page which tries to infect victim computers with malware via JavaScript file, called firefox-patch.js. The redirect page aims to convince users that they should immediately update their version of Firefox and display a pop-up which automatically shows a prompt to save the patch file or automatically open it. The JavaScript file itself is reported by security researchers to be a well-known Trojan Horse infection, going by the name Kovter, which was reported mainly to be associated with such fake updates as a mean of distribution. If you believe that your computer has been infected by the Kovter Trojan or if you keep seeing the “Critical Firefox Update” screen appearing, we recommend that you read the following article as it aims to help you secure your computer.

Threat Summary

NameCritical Firefox Update (Kovter Malware)
Short DescriptionDisplayed by a fake web page, the Kovter trojan aims to steal information from the infected computers.
SymptomsYour web browser may display a web-page , headed “Critical Firefox Update”. It asks you to download a .js file, which is the malware infection module.
Distribution MethodVia a fake Firefox Update page.
Detection Tool See If Your System Has Been Affected by Critical Firefox Update (Kovter Malware)


Malware Removal Tool

User ExperienceJoin Our Forum to Discuss Critical Firefox Update (Kovter Malware).

Critical Firefox Update Page – Distribution Methods

In order for you, the user to see it, the Critical Firefox Update page may be spread as a result of either visiting a web page, which causes a redirect to it or as a result of having adware or a similar unwanted program on your computer.

If it infects your computer as a result of a web page, then be advised that this page is either malicious or a compromised legitimate one. It often happens that cyber-criminals tend to intercept traffic from legitimate web pages to display their redirects and infect victims and they often target sites with bad security practices.

If however you see all sorts of redirects and pop-ups of such type, then it is very likely that you may have started seeing this web page as a result of having a PUP (potentially unwanted program) that is install on your OS. These types of PUPs often pretend to be legitimate helper programs, but their main goal is to display ads that generate money to their developers via suspicious pay-per-click schemes.

Critical Firefox Update and Kovter Trojan – More Information

When you see the Critical Firefox Update page, you may immediately notice a pop-up alongside it, asking you to download firefox-patch.js:

This .js file is the infection file of the Kovter Trojan horse. The Kovter Trojan is a threat that exists since the first appearances of the Police type of ransomare viruses. The virus has evolved in a more sophisticated variant since then that injects a JavaScript code onto victims computers.

When an infection with Kovter malware commences, the virus first triggers a dropper which drops malicious files in %AppData% and %Local% directories. This activity results in the Kovter malware being able to create a registry entry that triggers a maicious shell code in Widnows PowerShell and causes a restart, sealing it’s infectionas successful. The outcome of this after Kovter restarts is a file, called regsvr32.exe or similar fake Windows process name to run with administrative priveleges on the infected machine.

The outcome of this is that Kovter is capable to perform the following activities on a compromised computer:

  • Display advertisements and connect the victim PC to various third-party hosts.
  • Take screenshots on the compromised machine.
  • Obtain passwords.
  • Steal files from the computer it has infected.
  • Record sound or video from the camera and microphone.
  • Log the keystrokes you type.

Remove Critical Firefox Update and Kovter Troaj from Windows

If you want to remove the Kovter Trojan from Windows, we strongly suggest that you follow the removal instructions underneath this article. They have been divided in manual as well as automatic removal instructions with their main goal being to help you remove this virus according to your personal experience and preferences, concerning malware removal. Furthermore, if manual removal does not seem to be helpful, an automatic removal is also strongly advisable. According to security experts, the most effective method for automatic removal is to download and run a scan using an advanced anti-malware software. It will help you to automatically remove the Kovter malware and the software that may be causing such redirections to appear on your PC and also ensure that future protection is also available.


Ventsislav Krastev

Ventsislav has been covering the latest malware, software and newest tech developments at SensorsTechForum for 3 years now. He started out as a network administrator. Having graduated Marketing as well, Ventsislav also has passion for discovery of new shifts and innovations in cybersecurity that become game changers. After studying Value Chain Management and then Network Administration, he found his passion within cybersecrurity and is a strong believer in basic education of every user towards online safety.

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