For more than the last three decades, the security of software systems has been an important area of computer science, yet it is a rather recent general recognition that technologies for software security are highly needed.This book assesses the state of the art in software and systems security by presenting a carefully arranged selection of revised invited and reviewed papers. It covers basic aspects and recently developed topics such as security of pervasive computing, peer-to-peer systems and autonomous distributed agents, secure software circulation, compilers for fail-safe C language, construction of secure mail systems, type systems and multiset rewriting systems for security protocols, and privacy issues as well.