This document discusses botnets, which are networks of compromised computers remotely controlled by attackers to conduct illegal activities without the owners' knowledge. It aims to determine defenses against botnets by investigating detection strategies and countermeasures. The author developed and implemented a botnet called Solar to better understand botnets and help develop defensive strategies. Detection techniques discussed include intrusion prevention systems, next-generation firewalls, and honeynets. Countermeasures focus on disrupting command-and-control infrastructure through traffic filtering, sinkholing domains, and shutting down malicious servers.