In December 2015, a threat actor compromised power distribution companies in western Ukraine, causing a power outage for more than 230,000 residents. Several control centers were targeted by suspected Russian hackers, who were able to siphon operator credentials and gain access to the power grid for the Ivano-Frankivsk region. The power outage lasted as long as six hours in some areas. During the outage, threat actors also flooded customer services phone lines with calls to prevent customers from reporting the incident. The compromise of the Ukrainian power grid was an escalation from previous disruptive incidents and the first confirmed cyber operation to successfully take down energy infrastructure. The incident set an ominous precedent for the security of power grids around the world. The electricity distribution system in Ukraine was again targeted in 2016.