Recent Windows 10 November Update (Threshold 2) has added ‘Scan With Windows Defender’ option to right click menu. When Windows 10 was launched on July 29, this year, ‘Scan with Windows Defender‘ context menu option for the selected file or folder or drive was not offered by Microsoft.
Though Windows Defender offers real-time protection, which blocks known viruses and threats in real-time, Windows 10 really lacks a right-click scan option when was needed by user to perform a removable or USB drive scan.
This option was not available in insider builds from the beginning either, recently it was added to an preview build, followed to RTM build with the release of November Update (Threshold 2).
Interestingly, this option still appears active and enabled (but not grayed out) even when a 3rd-party antivirus was already installed on Windows 10, selecting it, causes Windows Defender to show ‘This app has been turned off and isn’t monitoring your computer’, that’s understandable and is the intended (default) behavior. Trying to launch Windows Defender from the Start or search also shows that error.
When you close that dialog, you’ll receive another warning: ‘Windows Defender was unable to scan the selected file(s).