This policy setting allows you to configure the automatic scan which starts after a definition update has occurred. If you enable or do not configure this setting, a scan will start following a definition update. If you disable this setting, a scan will not start following a definition update. Fix: (1) GPO: Computer Configuration\Administrative Templates\Windows Components\Windows Defender\Signature Updates!Turn on scan after signature update (2) REG: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Signature Updates!DisableScanOnUpdate