Framework and principles for active cyber defense.

This essay offers a broad view of active defense derived from the concept of active air and missile defense. This view admits a range of cyber defenses, many of which are widely deployed and considered essential in today's threat environment. Instead of equating active defense to hacking back, this wider interpretation lends itself to distinguishing different types of active defense and the legal and ethical issues they raise. The essay will review the concepts of active and passive air and missile defenses, apply them to cyberspace, describe a framework for distinguishing different types of active cyber defense, and finally suggest legal and ethical principles for conducting active cyber defense.