This book focuses on explaining the steps to analyze and understand systems security from both holistic and specific how-to perspectives. It will define risk-driven security, protection mechanisms and how to best deploy them, and present ways to implement security in a usable and user-friendly manner. The theme of all topics will be E-commerce and specifically mobile commerce. Some important topics covered in this book are: Users, users, users. Security that is difficult to use, albeit bullet-proof, will not be adopted by users. How to design and implement a strong security that is also user-friendly. What makes E- and M-commerce secure and how to design and implement? Techniques to implement an adaptive, risk-driven, and scalable security infrastructure. Fundamentals of architecting E- and M-commerce security infrastructure with high availability and large transactional capacity in mind.