Starting with the February 9, 2016 monthly updates, a computer running Windows 7 or Windows 8.1 that is configured to automatically install software updates from Microsoft will attempt to upgrade the computer to Windows 10 AUTOMATICALLY.
To prevent this from happening, it is unfortunately necessary to disable automatic installation of Microsoft's software updates and ensure that several previous updates related to Windows 10 are not installed on your computer. Here are the instructions necessary for Windows 7.
Step 1: removing unwanted updates
1) Click on the Windows icon in the bottom left corner of the screen to open the Start Menu, then select "Control Panels" from the column on the right.
2) Select the "Programs & Features" contol panel. If you don't see it on this screen, click on the "View by:" field near the top right corner of the window and change it to "Large Icons".
3) Within the "Programs & Features" control panel, in the column on the left, select the "View installed updates" option.
4) Windows will now compile a list of all previously installed updates. This takes a minute or two to finish (note the green progress bar at the top of the window).
5) Once the list is complete, Click on the "Name" field immediately above the list. This organizes the updates by name.
6) Scroll down towards the bottom of the list to where the updates named "Update for Microsoft Windows" appear. Find these two updates:
Update for Windows 7 (KB3068708) Update for Windows 7 (KB3035583)
When you find them, right click on them and select the "Uninstall" option. It is not necessary to reboot your computer until you've finished uninstalling them all.
Step 2: Disable automatic installation of Microsoft updates
1) Click on the Windows icon in the bottom left corner of the screen to open the Start Menu, then select "Control Panels" from the column on the right.
2) Select the "Windows Update" contol panel. If you don't see it on this screen, click on the "View by:" field near the top right corner of the window and change it to "Large Icons".
3) In the "Windows Update" control panel, click on the "Change setting" option in the column on the left.
4) Change the "Important Updates" field to "Check for updates but let me choose whether to download and install them".
5) Uncheck the box for the field "Give me recommended updates the same way I receive important updates"
6) Click the "OK" button to save the changes.
This unfortunately means that desirable security updates won't get installed on your computer, but the alternative of having Windows 10 potentially wreck your computer with botched install (or a botched uninstall, which has happened to one person here) is worse. You *can*, however, manually install security updates once a month, deselecting the updates related to Windows 10.
Step 3: Manually install necessary updates (done monthly)
1) Click on the Windows icon in the bottom left corner of the screen to open the Start Menu, then select "Control Panels" from the column on the right.
2) Select the "Windows Update" contol panel. If you don't see it on this screen, click on the "View by:" field near the top right corner of the window and change it to "Large Icons".
3) If you have previously configured Windows Update using the instructions above, the Windows Update control panel will tell you that "X important updates are available". Click on that line.
4) The resulting window will show you each update Windows wants to install. Among the list, you will find these two updates:
Update for Windows 7 (KB3068708) Update for Windows 7 (KB3035583)
These two updates are related to Windows 10. Right click on each of these updates and select "Hide Update". Once you've done this for both updates, click the "OK" button.
5) Back at the Windows Update control panel, you can now click on the "Install Updates" button. All of the non-Windows 10 updates will then install, after which a reboot is usually necessary.
Please note that Microsoft normally releases updates the second Tuesday of each month. Installing the updates towards the end of that week is recommended. Also please note that every time you run Windows Update, the two updates listed above will unhide themselves. As such, it is necessary to repeat step 4 every time you run Windows Update.