This server runs a version of the GNU / Linux operating system that I have personally customized, derived from RedHat Linux.
Each component of the OS was chosen and tuned for the highest reliability and security.
Thank you Richard Stallman for the Free Software Foundation, the GNU project, and the GNU Public License.
Thank you Linus Torvalds for the Linux Kernel.
Thank you Dan J. Bernstein for the qmail email server, and the djbdns DNS server, and all the supporting utilities.
Web pages are served by the Apache Web Server, with the php scripting language and the MySQL database engine.
Encrypted connections provided by OpenSSL and OpenSSH.

We have been online since January 2000, and have never had a security breach. (That's not a challenge.)