This policy setting allows you to enable real-time definition updates in response to reports sent to Microsoft MAPS. If the service reports a file as an unknown and Microsoft MAPS finds that the latest definition update has definitions for a threat involving that file the service will receive all of the latest definitions for that threat immediately. You must have configured your computer to join Microsoft MAPS for this functionality to work.If you enable or do not configure this setting real-time definition updates will be enabled.If you disable this setting real-time definition updates will disabled.
Windows Components\Windows Defender\Signature Updates
At least Windows Server 2012 Windows 8 or Windows RT
HKLM\Software\Policies\Microsoft\Windows Defender\Signature Updates!RealtimeSignatureDelivery