Actually it is a feature which comes built-in with Windows 10 operating system. This feature is called "Inactive Window Scrolling". It allows users to scroll inactive program windows using mouse wheel or arrow keys on keyboard by just hovering over them. Users don't need to click on inactive program windows. They just need to move mouse cursor over inactive windows and then they can scroll over them using mouse wheel or arrow keys.
This feature was not present in previous Windows versions such as Windows XP, Vista, Windows 7 and Windows 8/8.1. Users had to use 3rd party software to enable this feature in old Windows versions. Microsoft added this helpful feature to Windows 10 exclusively.
To better understand this feature, I'll give an example. Suppose you are visiting a website in your web browser. At this time your web browser window is active window. Now you open another program such as This PC. It'll immediately make This PC an active window and your web browser window will automatically become inactive or non-focused window as it'll lose focus. With the help of "Inactive Window Scrolling" feature, you can just hover over inactive web browser window with your mouse and then you can scroll in web browser window using mouse wheel or arrow keys without clicking on the window. So This PC is still active window but you can scroll inside an inactive window without clicking on it with the help of this feature.
What "Alina" was doing? She was accidentally moving the mouse over inactive window and as soon as she tried to scroll the active window, it actually scrolled inside inactive window as the mouse cursor was over inactive window.
Fortunately Windows 10 allows users to disable or turn off this feature. So if you also face this problem in Windows 10, you can disable this feature to fix this annoying issue.
Following steps will help you in disabling "Inactive Window Scrolling" feature in Windows 10:
1. Open Settings app from Start Menu or by pressing WIN+I keys together.
2. Now go to "Devices -> Mouse" section.
PS: Alternatively, You can directly launch this page using "ms-settings:mousetouchpad" command in RUN dialog box as mentioned here.
3. Now in right-side pane, look for "Scroll inactive windows when I hover over them" option.
To disable "Inactive Window Scrolling" feature, set the toggle button to OFF.
That's it. Now Windows 10 will never scroll inactive non-focused windows. You'll need to click on the windows first to make them active and then you'll be able to scroll inside them. Now no more accidental scroll occur in Windows 10.
