This book is a practical guide to find and exploit security weaknesses in web applications. This book is very practical in focus, and describes in detail the steps involved in detecting and exploiting each kind of security weakness found in a variety of applications such as online banking, e-commerce and other web applications. Because every web application is different, attacking them need to bring to bear various general principles, techniques and experiences in ways that imaginative. The authors are professional penetration testers who have been involved in web application security for nearly a decade.