Windows is always going to give you a potential Virus warning for any unlicensed software.
As we are a nonprofit volunteer project it would not be worth it to buy an official game license, which is why you will have to simply ignore the Virus warning.
There should be an option to open the .exe nonetheless in the Warning screen. Just click that and you are good to go.
I understand that we are simply a person on the internet, so I do not judge you for being too careful. You can always check out our youtube playthrough recording as well!