Back in 2012, I was pleased to receive an invitation to a conference that Jens, Kevin Govern, and Claire Finkelstein were hosting on the law and ethics of cyberwar.  It was a great conversation; so great, in fact, that Jens and his colleagues were inspired to use it as the launching pad for this volume — Cyberwar: Law and Ethics for Virtual Conflicts.  They asked me to write a chapter on an idea I’d been thinking about since my first foray into the cyber arena back in 2007 — whether and when IHL (international humanitarian law, or the law of armed conflict for those of you trained in the United States) might involve a duty to hack?  The basic idea was straightforward — if a cyber-operation could achieve a military objective (say disabling a power grid or a war-supporting factory’s operations) without killing anyone or causing any lasting damage to the facility, shouldn’t IHL require States to employ it in lieu of kinetic operations that might cause civilian casualties or property damage? Looking at the …