Some of the malicious programs want to make sure that you cannot use any anti-virus software to clean the malware. In order to do this, they block all the known security software in Windows so that you can neither download the security software nor you can install it in Windows. This is done by adding the URL entries in the HOSTS file to prevent you from accessing the websites of the security products vendors. And some malware also add the certificates of security software to the untrusted store making it impossible to install the security software belonging to these valid companies.
If you are having difficulty downloading or installing anti-virus or anti-malware products of various reputed companies in your Windows PC after a malware infection, you can use the free AVCertClean program. It can scan through the certificates stores in your Windows PC and check if the untrusted store has a valid certificate belonging to any security software company. If any such certificates are found, then AVCertClean also offers the option to remove them so that you can proceed with the installation of security products.
You can download AVCertClean and double-click on to launch it. It scans your system very quickly and in a matter of seconds shows you the results. If no certificates are found in the untrusted store, then it will tell you so and it is usually a good thing to not find any certificates in the untrusted store. A log file is also created to save the activities of the AVCertClean. If it does find a matching certificate belonging to a known security vendor then it will try to fix it and remove that certificate. Afterwards you can reboot your PC and install the security software to keep your PC protected from malware.
Conclusion: AVCertClean removes the certificates belonging to known security vendors from the untrusted certificates store in Windows. This will help you fix any issues that are preventing you from installing security software in Windows.
You can download AVCertClean from https://toolslib.net/downloads/viewdownload/385-avcertclean/.