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#11
Wow. There is a huge amount of info being discussed in this topic. Good questions.
You are not the only user of your computer. Every time you allow the Windows operating system to update itself, a "user" named TrustedInstaller goes to work. For your protection, TrustedInstaller is not allowed access to your user generated files. System is another "user". I'll leave it at that for simplicity.
Do you have the User Account Control set to the default value?