Check for the latest virus and spyware definitions before running a scheduled scan This policy setting allows you to manage whether a check for new virus and spyware definitions will occur before running a scan. This setting applies to scheduled scans as well as the command line 'mpcmdrun -SigUpdate', but it has no effect on scans initiated manually from the user interface. If you enable this setting, a check for new definitions will occur before running a scan. If you disable this setting or do not configure this setting, the scan will start using the existing definitions.

(1) GPO: Computer Configuration\Administrative Templates\Windows Components\Windows Defender\Scan!Check for the latest virus and spyware definitions before running a scheduled scan (2) REG: HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows Defender\Scan!CheckForSignaturesBeforeRunningScan