Jerry,
I can't really comment on automatic upgrades from Win 7 to Win 8.1, as I don't have knowledge/experience with it.
However, there is a similar issue with Win 7, Win 8, or Win 8.1 that they periodically check back with Microsoft (automagically) to see if
Windows 10 has been released (most users probably have this "check" installed and you can see it in Task Manager called GWX.exe). I can only assume that once Win 10 is released, users would be presented with an option to upgrade to Win 10, rather than just having it happen. To be certain that doesn't automagically happen to me, I've uninstalled (and hidden) the Windows Update for KB3035583. You can disable this check for Windows 10 (if you choose) by reading and following the directions on this web page:
https://tweakhound.com/2015/04/08/gwx-get-windows-10/I only discovered this when I recently investigated my Win 8.1 machine pauses and researched the GWX.exe that I didn't recognize in my Task Manager.
I'm guessing that what TPAnderson experienced was a result of Windows Updates that are automatically downloaded and installed - the default for Windows setups. I believe all Win 8.0 would automagically be updated to 8.1, but it's not really a new operating system - it's just updates to 8.0. I think I've heard others mention that Win 7 was updated to 8.1 without their consent, but I really didn't pay much attention to it. It hasn't happened to my Win 7 (32bit) installation, and I have installed (by choice) all of the Windows updates that have been presented on my Win 7 machine. My set up is for me to be notified of the update but I will choose whether to download and install the update. You can see what the updates do by searching the KB# on the web, but sometimes that simply leads to more and more digging about the update (like KB3035583 and
https://support.microsoft.com/en-us/kb/3035583 ). Frankly, most people won't have the inclination to keep digging to see what such updates do.
My suggested solution for preventing unwanted automagic updates of your OS is turn off the automatic download and installation of said updates. You'll then have to turn off the incessant warnings by Windows Defender that "Automatic Updates aren't enabled" or something similar (or tell Windows Defender to not warn you about that anymore). You may also have to dig into each update more thoroughly before deciding whether to install it or not. All-in-all, it's just more work for the end user. Not a great solution ....
Armand