Computers are an integral part of our economic, social, professional, governmental, and military infrastructures. They have become necessities in virtually every area of modern life, but their vulnerability is of increasing concern. Computer-based systems are constantly under threats of inadvertent error and acts of nature, as well as those attributable to unethical, immoral, and criminal activities. It is the purpose of this Computer Security Handbook to provide guidance in eliminating these threats where possible, and if not, then to lessen any losses attributable to them.