Genesis and Theory of Computer Viruses -- The Formalization Foundations: from Turing to von Neumann (1936 – 1967) -- F. Cohen and L. Adleman’s Formalization (1984 – 1989) -- Taxonomy, Techniques and Tools -- Fighting Against Viruses -- Learning Computer Viruses by Programming -- Computer Viruses in Interpreted Programming Language -- Companion Viruses -- Worms -- Computer Viruses and Applications -- Computer Viruses and Applications -- BIOS Viruses -- Applied Cryptanalysis of Cipher Systems: The YMUN20 Virus -- Conclusion -- Conclusion.“Viruses don’t harm, ignorance does. Is ignorance a defense?” herm1t “[...] I am convinced that computer viruses are not evil and that programmers have a right to create them, to possess them and to experiment with them ... truth seekers and wise men have been per- ´ secuted by powerful idiots in every age ...’ Mark A. Ludwig Everyone has the right to freedom of opinion and expression; this right includes freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers. Article 19 of Universal Declaration of Human Rights The purpose of this book is to propose a teaching approach to under- 1 stand what computer viruses really are and how they work. To do this, three aspects are covered ranging from theoretical fundamentals, to pr- tical applications and technical features; fully detailed, commented source 1 We will systematically use the plural form “viruses” instead of the litteral one “virii”. The latter is now an obsolete, though gramatically recommended, form. VIII Preface codes of viruses as well as inherent applications are proposed. So far, the applications-oriented aspects have hardly ever been addressed through the scarce existing literature devoted to computer viruses.