This is almost certainly Windows Defender. It has been more and more of a problem in recent months. It could be other antivirus software as well, but Windows Defender is the most common culprit. Temporarily suspend such software while downloading, installing and activating. Turn it on again after everything is running properly.
If you only have Windows Defender, press the Start button and start typing "Defender" -- you'll see an option for Windows Defender Settings. Click that and then click the button to "Turn off Windows Defender Antivirus." If the button instead says "Turn on Windows Defender Antivirus" then you have a different antivirus software running and need to disable that instead using its publisher's directions.
These programs aren't perfect. If they were, they wouldn't give you an option to turn them off when they get in the way of things you actually do want to do.