On December 23rd, 2015 a cyber attack was launched against the Ukrainian Power Grid and caused a power outage to over 230,000 customers. This was the first public cyber attack in history to successfully take out the power. What followed was a months long investigation into determining what happened and how it occurred that took place by teams around the world. In this presentation, one of the investigators on the case will present his and the SANS Institute's findings and give recommendations on securing industrial control system (ICS) networks like the power grid.