The aim of this text book is to discover software bugs that pose cyber security threats and to explain how to fix the bugs to mitigate such threats. It elaborates cyber attack scenarios in web browsers and web servers and explains mitigation of such threats. It focuses on mobile software bugs posing cyber security threats and mitigation techniques. The purpose of this book is to articulate the urgent need for cyber security in critical computer systems, networks, and World Wide Web, and to explain various threat scenarios. The book articulates well known cyber attack incidents, explains the attack scenarios, and explores mitigation techniques.