The NSA has done some security work with Linux. They refer to it as
"Security-Enhanced Linux". It is an ongoing project.
http://www.nsa.gov/selinux/index.html
(Pulled from the web site.)
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Security-Enhanced Linux Project Background
Researchers in the Information Assurance Research Office of the National
Security Agency (NSA) worked with Secure Computing Corporation (SCC) to
develop a strong, flexible mandatory access control architecture based on
Type Enforcement, a mechanism first developed for the LOCK system. The NSA
and SCC developed two Mach-based prototypes of the architecture: DTMach and
DTOS. The NSA and SCC then worked with the University of Utah's Flux
research group to transfer the architecture to the Fluke research operating
system. During this transfer, the architecture was enhanced to provide
better support for dynamic security policies. This enhanced architecture was
named Flask. The NSA is now integrating the Flask architecture into the
Linux operating system to transfer the technology to a larger developer and
user community.
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There is also a spin off to SourceForge.
http://selinux.sourceforge.net/
http://sourceforge.net/projects/selinux/
