Fix: Virus has Change all file Extensions on my Windows 10 PC


One of our readers reported that all the file extensions have changed to some unknown file format. If so, it could be a virus! If all the file extensions have been modified to unknown applications by a virus, then restore the default file extensions, formats & icons to their original state.

On my PC, all the file extensions have changed; is this a virus?

You may have mistakenly set the default files option to something else. If this happens to all, however, it is best to first search your PC with an antivirus before doing something else. For better performance, it can be Windows Defender at Boot timer or someone you use in Safe Mode. To be doubly certain, you can also use a second-opinion portable scanner. 

Also Read: Here's How You Can Access Control Panel in Windows 10 (20H2)

If the scan is clear, or you have been able to delete all the corrupted files that caused the issue, then it's time to reset the default association so that it can open in the application you specified. One after the other, try these approaches. To fix it, you will need admin authorization.

  • Reset Defaults in Windows 10 Settings
  • Delete UserChoice folder
  • Reset via File Association Fixer.

In Windows 10 Settings, reset Defaults

The file extensions have all modified on my PC. A virus, is it?

Open Settings (Win + I) on Windows 10, then go to Applications > Default Apps.

Scroll down until you see Reset Recommended Defaults for Microsoft and press the Reset button.

By going to the classic Control Panel > Default Programs, you can do this, too. It will carry you to the same place, though.

Delete folder for UserChoice

File Association for User Preference Folder

If this does not succeed, first establish a restoring point for the device and then try this:

Open Regedit (Use Win + R to open the Run prompt and type regedit, followed by pressing Enter)

Then navigate to the key below:

HKEY CURRENT USER\Microsoft\Windows\CurrentVersion\Explorer\FileExts\Software\Software

FileExts expansion. You'll see a list of folders for file extensions here.

You'll need to expand each of them, one after the other, and remove the UserChoice folder if you see the UserChoice folder under it.

Reset via File Fixer Association

You can download File Association Fixer v2 or freeware, and manually restore each file association. As we saw above, because of a compromised registry, broken file associations are usually caused. You can help repair it with this software.

I hope it was easy to follow the message, and you can solve the File Association problem. If the virus was not a concern, it may have been triggered by either a software installation or manual intervention and you may be forced to use this PC option to reset.

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