It is becoming more common for researchers to find themselves in a position of being able to take over control of a malicious botnet. If this happens, should they use this knowledge to clean up all the infected hosts? How would this affect not only the owners and operators of the zombie computers, but also other researchers, law enforcement agents serving justice, or even the criminals themselves? What dire circumstances would change the calculus about what is or is not appropriate action to take? We review two case studies of long-lived malicious botnets that present serious challenges to researchers and responders and use them to illuminate many ethical issues regarding aggressive mitigation. We make no judgments about the questions raised, instead laying out the pros and cons of possible choices and allowing workshop attendees to consider how and where they would draw lines. By this, we hope to expose where there is clear community consensus as well as where controversy or uncertainty exists.