Your Windows installation is insecure full stop. No matter when you patched. Even if all vulnerabilities would be patched then there are still backdoors siting and waiting to be exploited.
So is your Android, iOS, macOS and every linux flavour out there. What's so special about Windows being insecure?
Closed-source just ups the uncertainty about security. I'm not saying open source is a panacea, but I think in general it increases certainty about security to some extent.