This book is geared at postgraduate courses on managing and designing information systems. It concentrates primarily on security in military systems and looks at the different goals organisations might have in employing security techniques and which techniques are best suited to acheiving certain goals. The book provides answers to questions such as What is security? and What are the security problems particular to an IT system? It is essential reading for students on final year undergraduate courses and MSc courses on Infomations Systems, Management of Information Systems, and Design of Information Systems. The text is up-to-date and includes implications which arose from the Y2K date change.