Researchers at IBM and Aesec Corp released a paper looking at Multics Operating System security and the penetration analysis that was done by the Air Force in the 1970’s. Multics received a B2 security rating from the NSA (A1 being the highest rating), which is a rating far above todays operating systems commonly in use (Windows NT is rated as C2). What’s interesting to me is that Multics (even after its security enhancements) was deemed unacceptable for systems in an open environments (i.e. being connected to a network like the Internet).

Here’s a link to the paper (PDF)