Botnets, consisting of thousands of interconnected, remote-controlled computers, pose a big threat against the Internet. We have witnessed the involvement of such malicious infrastructures in politically motivated attacks more than once in recent years. Classical countermeasures are mostly reactive and conducted as part of incident response actions. This is often not sufficient. We argue that proactive measures are necessary to mitigate the botnet threat and demonstrate techniques based on a formalized view of botnet infrastructures. However, while being technically feasible, such actions raise legal and ethical questions.