The data security study at the four sites -- The Massachusetts Institute of Technology (MIT), the State of Illinois, TRW Systems, and IBM at Gaithersburg, Md. -- was undertaken to (1) build a sound body of knowledge about computer system data security to enable users and manufacturers to better understand the subject, problems, and priorities; and (2) gain some practical 'hands on' experience of the effect on costs and productivity and the organizational impacts of adding data security measures to existing installations. The study sites had somewhat different task assignments, but all of the sites implemented an experimental IBM-developed software product called Resource Security System, which addresses the problems of access control, integrity, and journaling. The State of Illinois studied the economic impact of imposing data security objectives on an existing installation and the ease of use of certain security features, while MIT evaluated the needs of several industries and studied the technical aspects of authorizing users' access to data in computer systems. TRW sought the means of certifying a computer system as secure and also documented what features and functions computer systems require to counteract potential vulnerabilities. The IBM site studied problems related to installing a secure operating system in an ongoing data processing environment. Findings at each of the study sites are summarized, and the report concludes with a discussion of what managers can do to address a data security problem. For other volumes dealing with the work at the study sites, see NCJ 89627-32 and 89655-60.