This policy setting allows you to configure definition updates on startup when there is no antimalware engine present. If you enable or do not configure this setting, definition updates will be initiated on startup when there is no antimalware engine present. If you disable this setting, definition updates will not be initiated on startup when there is no antimalware engine present. Counter Measure: Configure this setting depending on your organization's requirements. Potential Impact: Definition updates will be initiated on startup when there is no antimalware engine present, which may affect startup time. Fix: (1) GPO: Computer Configuration\Administrative Templates\Windows Components\Windows Defender\Signature Updates\Initiate definition update on startup (2) REG: HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows Defender\Signature Updates!DisableUpdateOnStartupWithoutEngine