At the moment, I'm running Vista X64 with Win Def version 1.1.16000, using Engine 1.1.15000, and Definition 1.271.139.
So it can be done. Follow the link Devilus supplied https://www.microsoft.com/en-us/wdsi/definitions, then go down to the
line "Windows Defender in Windows 7 and Windows Vista 32-bit|64-bit" and click on the appropriate choice.
Download a file named mpas-fe,exe. Right click on it, and run as administrator. You won't anything happen visibly, but
afterwards you can fire up Win Defender from your Start menu and verify the new Engine and Definition numbers.
Alternatively, you can go the Major Geeks website and download the latest Win Defender definitions from there.
Edited by mike_shupp, 27 June 2018 - 05:26 PM.