Read the EULA before you click ok... or don't complain afterwards.

It is clearly stated in the EULA (or an addendum to the EULA depending of Windows version) that Microsoft can and will change files on the computer without the users knowledge whenever they find it necessary.

It is furthermore stated that the user do not own the operating system or any components of it.

Noone has ever tried the EULA in a court of law...

btw. I don't care... I got tired of Microsoft and changed to something better.