Conclude with a personal statement recommending what an IT professional should do with this information. An essential part of a general$-$purpose computer utility system is a set of protection mechanisms which control the transfer of information among the users of the utility. The Multics system$*,$ a prototype computer utility~ serves as a useful case study of the protection mechanisms needed to permit controlled sharing of information in an on$-$line, general$-$purposes information$-$storing system. This paper provides a survey of the various techniques currently used in Multics to provide controlled sharing, user authentication, inter$-$user isolation, supervisor$-$user protection, user$-$written proprietary programs, and control of special privileges. Controlled sharing of information was a goal in the initial specifications of Multics $[8,$ ii$],$ and thus has influenced every stage of the system design, starting with the hardware modifications to the General Electric $635$ computer which produced the original GE $645$ base for Multics. As a result, information protection is more thoroughly integrated into the basic design of Multics than is the case for those commercial systems whose original specifications did not include comprehensive consideration of information protection. Multics is an evolving system, so any case study must be a snapshot taken at some specific time. The time chosen for this snapshot is summer, $1973$~ at which time Multics is operating at M$.$I.T$.$ using the Honeywell $6180$ computer system. Rather than trying to document every detail of changing environments this paper concentrates on the protection strategy of Multics, with the goal of communicating those ideas which can be applied or adapted to other operating systems