It works if I ingore the warning but still strange.
[0.17.1] Window defender mistrusts factorio installer
Re: [0.17.1] Window defender mistrusts factorio installer
Thanks for the report. This isn't something we directly control (our release process is no different than 0.16 or previous). I suspect it will just take some time for Microsoft to update their filter(s) for these false positives.
If you want to get ahold of me I'm almost always on Discord.