Personally, I use linux. Much like medicine, the "secrets" as to how the system works is available for free, and constantly undergoes security audits. Newer distributions make linux as easy to use as Windows, and adds far greater stability. In fact, one machine I have running, has been up for over 500 days without a reboot. Although there have been many security updates for this machine, that have required a reboot, I have not applied them, because the machine is on a private network, not connected to a LAN, and serves a single purpose.