This book is designed for use in courses on Ethical Hacking & its Methodology at the undergraduate/postgraduate level, particularly designed for the structured curriculum of Bachelor of Technology- Computer science & Engineering The book is organized into five sections. Section 1 covers the basics of ethical hacking, limitations, security testing, ethics along with legal aspects. Section 2 covers the hacking methodology, sniffers, session hijacking, denial of service (DoS), basics of web server, web server hacking and web application hacking. Section 3 discusses web and network hacking, sql injection, wireless hacking, viruses & worms, physical security, analysis about linux and linux hacking. Section 4 discusses the social engineering, steps involved in social engineering, social engineering attack, impacts of social engineering, fundamentals of physical penetration attacks, penetration testing and its types. Section 5 includes the concepts of legal system, security architecture of windows, brute force attack, rainbow table attack, creating backdoors for windows, mobile hacking - SMS & call forging, Caller id forging / spoofing, SMS routing in GSM and bluesnarfing.