This research project has produced an innovative architecture and corrresponding engineering prototype consisting of trusted security services and integrated operating system mechanisms for the protection of distributed multi-domain computing environments from malicious code and other attacks. These security services and mechanisms extend and interoperate with existing workstations, applications and open source operating systems, providing new capabilities for composing secure distributed systems using commercial off-the-shelf (COTS) components. The latter construct results from the realization that unless a secure system offers users comfortable and familiar interfaces for handling routine information, the secure system will fail due to lack of user acceptability. This work was supported in part by the MYSEA project of the DARPA/ATO CHATS program.