Abstract : As part of its continuing interest in the problem of how to improve computer security, the Advanced Research Projects Agency of the Department of Defense has funded a project, now under way at the University of California's Lawrence Livermore Laboratory, involving ways to measure, test, and evaluate the actual security of data stored in a computer system. This project, called RISOS (for Research in Secured Operating Systems), has, as its name indicates, a primary interest in finding out how operating systems can be made more secure. The focus of the project is on software security as opposed to physical security. Its goal is to develop detailed security guidelines that will be of value to both system design and system operation personnel.