This book introduces a new weapon in computer warfare which helps to collect more information about malicious websites, client-side exploits, attackers, and their proceeding. Client honeypots are a new technique to study malware that targets user client applications, like web browsers, email clients, or instant messengers. We introduce some of the more well-known client honeypots, how they work, and how they can be used to secure a computer network. Furthermore, the authors show a few of the most frequently used client application exploits and how they can be examined to get more information about the underground economy.