Was it a specific antivirus that flagged it, or was it Windows Defender saying that the program was untrusted? The latter often happens with unsigned Unity builds.
Also, ran the Win 64-bit build through VirusTotal and none of the antivirus vendors came back detecting anything: https://www.virustotal.com/gui/file/f6c5798cddf417dc2d6a6f382b1a207c080b535ab760...