Practical UNIX and Internet Security, 3rd Edition

What Is Computer Security?

Terms like security, protection, and privacy often have more than one meaning. Even professionals who work in information security do not agree on exactly what these terms mean. The focus of this book is not on formal definitions and theoretical models so much as it is on practical, useful information. Therefore, we’ll use an operational definition of security and go from there.

COMPUTER SECURITY. A computer is secure if you can depend on it and its software to behave as you expect.

If you expect the data entered into your machine today to be there in a few weeks, and to remain unread by anyone who is not supposed to read it, then the machine is secure. This concept is often called trust : you trust the system to preserve and protect your data.

By this definition, natural disasters and buggy software are as much threats to security as unauthorized users are. This definition is obviously true from a practical standpoint. Whether your data is erased by a vengeful employee, a random virus, an unexpected bug, or a lightning strike—the data is still gone. That’s why the word “practical” is in the title of this book—and why we won’t try to be more specific about defining what “security” is, exactly. A formal definition wouldn’t necessarily help you any more than our working definition, and would require detailed explanations of risk assessment, asset valuation, policy formation, and a number of other topics beyond what we are able to present here.

Our practical ...