I have deleted all files, extracted or zip, that I had previously. I'm wagering it's my antivirus system, but it seems multiple other people are now having that problem in the comments, so I'm not so sure. It doesn't download no matter what I try, unfortunately.
That's not the only way to play it though. You can add the game to Steam with the key on the download page, or use the itch.io app and download it from there.