Picture a cyber warfare arms race where the participating countries have spent years of building offensive cyber warfare capabilities by exploiting the monoculture on one another's IT infrastructure. Suddenly, one of the countries starts migrating to a hardened operating system of its own, and by integrating it on systems managing the critical infrastructure it successfully undermines the offensive cyber warfare capabilities developed by adversaries designed to be used primarily against Linux, UNIX and Windows. That's exactly what China is doing right now with their hardened OS Kylin according to Kevin G. Coleman, Senior Fellow and Strategic Management Consultant with the Technolytics Institute who presented his viewpoint in a hearing at the U.S. -- China Economic and Security Review Commission.
There is a PDF ( 23 pages - 253.4 KB (259462 bytes) ) regarding the FAA Audit.
FAA report on the penetration testing done against the FAA systems