It is impossible to measure the specific degree of security of any computer system. Added security features can be implemented, but computer security must be closely aligned with computer system reliability and clean design. A computer system that is easy to understand, is comprehensive, and uses relatively few machines to accomplish its services is less likely to be threatened than a more complex system. The report reviews security considerations for computer hardware and software and illustrates major weaknesses in contemporary operating systems. Accidental and deliberate threats to computer hardware and software are described as well as threat techniques for penetration. Ways to establish adequate safeguards against tampering by system users, the most serious security threat, are outlined. The paper also discusses the security ramifications from increasingly complex computer systems and advancing computer technology. Diagrams and eight references are supplied.