U.S. cyberintelligence firm iSight Partners said on Thursday it has determined that a Russian hacking group known as Sandworm caused last month's unprecedented power outage in Ukraine.
"We believe that Sandworm was responsible," iSight's director of espionage analysis, John Hultquist, said.
The conclusion was based on analysis of malicious software known as Black Energy 3 and KillDisk, which were used in the attack, and intelligence from "sensitive sources," he said.