On-demand Scanner by Windows Defender
There is no option to run a single-file scan using the context menu in Windows. You can only use it to run a quick, full or custom scan on folders or drives. Scanning networked drives is not an option and it will not protect or scan for files and folders in a home network.
When a malicious file or process is detected, the program will prompt the user for action or automatically use the default actions that Windows Defender has as per its rating. Regardless of the setting users have picked, the program will alert the user via its system tray icon so that they can review the details or manage the program. If Microsoft wants to further analyze a detection, a window with a list of detected items will be displayed prompting the user to decide whether to send or withhold the copy of detected files. Submitting the files to Microsoft is optional and the alert will be displayed even if you did not join Microsoft Spynet.
Microsoft Spynet is similar to the cloud-based protection offered by PrevX or Panda Cloud Antivirus. It will help other Windows Defender users if you submit detected files.
To test the scanner of Windows Defender, I allowed it to scan 239 executable malware files and 96 archive files.
Windows Defender has detected 90 executable files and 58 archive files with malware, leaving the computer at risk from 187 threats. However, like other anti-virus or anti-malware programs, Windows Defender provides on-access protection for malware that the on-demand scanner has failed to detect.