AVCertClean

Note: Some antimalware applications may trigger alerts for AVCertClean. However, out tests have shown that these are actually false positives, which means it's safe to download and use the tool.

SearchMaster, otherwise known as Trojan.Wdfload that, alongside many other harmful effects, can also forcefully set various code signing certificates as untrusted, even managing to block various security apps.

How to manually remove legit certificates from the Untrusted Certificates Store

That said, if you've encountered the "This program has been blocked for your protection" message for an app that hasn't triggered such alerts before, then, with a bit hardship, you might be able to do something about it.

For example, if you know what you're doing, you could bring up the "certmgr.msc" using your computer's Run console and manually delete the legit certificate that has found its way to the Untrusted Certificates store and reboot your computer for the changes to take place.

A simpler and much more practical solution, as an alternative

Or, you could use AVCertClean which, as its name kind of points out, automatically removes any legit certificate from the Untrusted Certificate Store. The tool requires no special treatment or extensive computer knowledge, for that matter, as you only have to download it on your computer and run it like any other app.

Once the app does its thing, you are presented with a logfile where you can view any changes or if any signed certificates have been removed from the Windows Untrusted Store, and that's really about it, no extra hassle involved. Of course, just like the first, aforementioned scenario where you have to manually remove the certificates, the changes will only take place after a system restart.

Share the log file with a person capable of helping you or send it to the email address from below

To end with, it's well worth pointing out that you can share the logfile to this email address if you require further assistance. Best of luck!