Want to secure your computer with the same techniques used by the National Security Agency? Turns out the NSA has published guides for securing Windows, Mac, Linux, and Solaris operating systems using methods that "are currently being used throughout the government and by numerous entities as
a security baseline for their systems."
It being a government organization, you'd expect the guides to be somewhat opaque or confusing, but the free PDFs, like Security Highlights of Windows 7 and Mac OS X 10.6 Hardening Tips, are actually well written primers to system security. They've put together several different security guides for each operating system, so put on your tin foil hats and hit up the main page to see how you stack up.
Security Configuration Guides
.