The Windows Defender command-line utility MpCmdRun.exe is prominently used for scheduling scans and updating the signature or definition files. The MpCmdRun.exe command usage info can be obtained by running MpCmdRun.exe with "/?" or without any parameter. However it doesn’t mention a useful switch that updates Windows Defender signatures and runs a Quick Scan at once. And this switch is not documented anywhere thus far.
Generally, if a feature or hidden "switch" in a software is not documented officially, there is a chance that the manufacturer may have missed updating the help files. However if you’re someone who doesn’t take anything for granted, you could test such hidden feature in a test computer, just in case. I’ve used and tested the undocumented SignatureUpdateAndQuickScan in my production computer, and the switch worked exactly as intended without any problems.
Signature Update & Quick Scan – Hidden Switch
To update the definitions and run a Quick Scan in one go, use the switch SignatureUpdateAndQuickScan (MpCmdRun.exe /SignatureUpdateAndQuickScan).
… and the event written to Microsoft-Windows-Windows Defender/Operational log.
This switch works in Windows 10 as well as in Windows 8 systems.
About the author
Ramesh Srinivasan founded Winhelponline.com back in 2005. He is passionate about Microsoft technologies and has a vast experience in the ITeS industry — delivering support for Microsoft's consumer products. He has been a Microsoft MVP [2003 to 2012] who contributes to various Windows support forums.