A sort of virtualization appeared four decades ago to perform multi-programming and simple time-sharing tasks inside a single mainframe. Virtualization became quickly the solution to limit cost and save money by server consolidation. Nowadays virtualization is a "hot topic" and it is habitually adopted in develop environments for testing and debugging purposes. This book presents a novel paradigm to secure personal computers. Virtualization is used to isolate the user system within a so-called security shell where multiple security services are configured to ensure the tamper resistance of the user''s environment. While conventional personal antivirus can be switched off, manipulated, or avoided by sophisticated malignant codes and technically experienced users, this antivirus enforces a continuous protection of the user''s environment from the security shell. The accesses to the file-system are real-time scanned and mobile/encrypted network connections are inspected. The whole system is finally protected by an encryption layer that inconspicuously encrypts the user system.