Global Internet threats are rapidly evolving from attacks designed solely to disable infrastructure to those that also target people and organizations. This alarming new class of attacks directly impacts the day to-day lives of millions of people and endangers businesses and governments around the world. For example, computer users are assailed with spyware that snoops on confidential information, spam that floods email accounts, and phishing scams that steal identities. At the center of many of these attacks is a large pool of compromised computers located in homes, schools, businesses, and governments around the world.

In this paper, the authors provide a detailed overview of current Botnet technology and defense by exploring the intersection between existing Botnet research, the evolution of botnets themselves, and the goals and perspectives of various types of networks. Authors also describe the invariant nature of their behavior in various phases, how different kinds of networks have access to different types of visibility and its strong impact on the effectiveness of any Botnet detection mechanism. A comprehensive picture of the various Botnet detection techniques that have been proposed is provided. Finally, the paper summarizes the survey and suggests future directions.