Some operating systems have achieved a certification from an external security auditing organization, such as a B2 or A1 CSC-STD-001-83 "Department of Defense Trusted Computer System Evaluation Criteria" or Common Criteria certification.
Note that meeting a given set of evaluation criteria does not make a computer operating system "secure"; nevertheless, it does imply a certain amount of care in its design and due diligence in its testing.
Trusted Solaris is a security-focused version of the Solaris Unix operating system. Aimed primarily at the government computing sector, Trusted Solaris adds detailed auditing of all tasks, pluggable authentication, mandatory access control, additional physical authentication devices, and fine-grained access control. Versions of Trusted Solaris through version 8 are Common Criteria certified. See [1] and [2] Trusted Solaris Version 8 recieved the EAL4 certification level augmented by a number of protection profiles. See [3] for explanation of The Evaluation Assurance Levels.
![[2]](http://wwws.sun.com/software/security/securitycert/images/TSol8_7-03CMS.jpg){kind=link}