Thanks to a recent post, I have learned that M$ uses an MD5 hash to check if files on your computer are up to date.
Originally posted here by Proactive
What happens is a lot of cheksums for the latest microsoft files are sent to your computer. Your machine checks if the cheksums are valid for your files. If they aren't, a message is sent back to microsoft about which files is out of date. Then the files are dowloaded and installed.
Where does Windows keep these checksums? Are they computed anew every time M$ checks for updates, or is a hard copy kept on the HD? Assuming they are kept on the HD, would it then be possible to keep checksums from the latest updates instead of the proper ones for your files to work around M$ automatically installing these updates?