In the previous chapters, we learned about computer networks, information system security, and intrusions and vulnerabilities. This information is important because the objective of this book is to give researchers and practitioners complete information about how to use honeypots and routers to collect Internet attacks. To meet this objective, researchers should have enough information about computer networks, which will help them to design a good network against the attackers. They should also have enough information about information system security, which will help them to know the most important issues in information security. Also, researchers should have sufficient information about intrusions and vulnerabilities, which will help them to know how the intrusions can exploit the vulnerabilities to compromise networks. This chapter discusses about malware; this discussion is important because we would like to collect Internet attacks (i.e., malware), so we must know the malware in detail.