If, like many, you have configured your Windows Firewall / any other 3rd party firewall to block all outgoing traffic you will find that Windows defender will be unable to update unless you allow port 80/443 (HTTP/HTTPS) for executable svchost.exe. However, this is a core Windows executable, and therefore you may wish to block this as it isn’t used by Windows Defender alone.
The solution therefore is to manually update your windows defender definitions using the following URLs:
The latest x86 / 32bit Windows Defender Updates are always available using this URL:
http://go.microsoft.com/fwlink/?linkid=70631
For x64 versions of Windows, use the following URL:
http://go.microsoft.com/fwlink/?linkid=70632
Finally, for Itanium version of Windows use the following URL: