The aim of this book is to develop a Multi-Level security model for web service computing environments. This book describes about an Hardware Level Authentication scheme of web service consumers for secure communication with the service providers and History based Accounting and Reacting Denial of Service attack (DoS) model to detect and prevent possible DoS attacks in web service computing. The main objectives of this book are to provide built in authentication for web service consumers. It also minimizes the security constraints and challenges in any close group web service communication. This book has engaged the E-learning framework as a test bed to carry out the experiments in support of the proposed idea and its goals. The E-learning framework provides all the possible aspects of web service computing to perform the experimentation of this book. The experimental results in this book reveal the performance and accuracy of the Two Tier Security Framework for SOS.