By Dustin Volz
WASHINGTON (Reuters) - The U.S. Department of Homeland Security said on Tuesday it was helping Ukrainian authorities investigate an apparent attack last month on the country's power grid that caused a blackout for 80,000 customers of western Ukraine's Prykarpattyaoblenergo utility.
Experts have widely described the Dec. 23 incident as the first known power outage caused by a cyber attack. Ukraine's SBU state security service has blamed Russia for the incident, while U.S. cyber firm iSight Partners linked it to a Russian hacking group known as "Sandworm."
(Reporting by Dustin Volz and Jim Finkle; Editing by Doina Chiacu)