Get Windows Defender warning on startup of latest version (Windows 10). I had to allow access to ‘Private networks…’ I did not get this with prior version. The ZwiftApp.exe should be digitally signed: 
This is the firewall, not app signing check. Normal behaviour on a lot of programs when getting an update.
Altough mine did not complain, maybe it was reset or you didnt use it on a public network before. This is just about adding an firewall exception for Zwift.