Hi - Windows SmartScreen flags this as unsafe. This could be because the Unity runtime that you're using is not recognised by Microsoft yet? Also it says that the publisher is unknown.

Hello, Ah thats annoying! Yes I suspect defender doesn't recognise it. I had this issue at work.

Try right clicking on the EXE and going properties, and then at the bottom it will say Unblock, click that and you should be good to go: