A central European security software company said on Monday that a cyber attack last month in Ukraine was more extensive than initially reported when the country’s secret police attributed Russia for a power outage.

Ukraine’s SBU state security service reacted by blaming the energy ministry as well as Russia in Kiev set up a commission to research the issue.

Similar malware was located in the networks of at least two other utilities while Prykarpattyaoblenergo was the only Ukraine electrical business that reported an outage, said Robert Lipovsky, senior malware research worker at Bratislava-based security business ESET.

“The reported case wasn’t an isolated event,” he said.

Prykarpattyaoblenergo openly attributed its outage on “hindrance” in the working of its own system. The Kremlin didn’t react to a request for opinion.

Research workers with iSight Partners and computer security companies Trend Micro said the evaluation of ESET the attackers sought to infect other utilities seemed credible, shedding new light on signs this is the first power outage shown to have been due to a cyber attack. Experts have warned for a long time, with growing urgency, that electric utilities are exposed to cyber attacks that could cut electricity.

“This is the very first time we’ve evidence and may connect malware to a specific outage,” said Trend Micro senior research worker Kyle Wilhoit. “It’s very frightening.”

Cyber company iSight Partners said that the report of multiple assaults of ESET is not inconsistent with its own investigation.

“There’s fairly strong consensus that there was a blackout resulting from computer network attack,” said iSight’s manager of cyberespionage investigation, John Hultquist.

Researchers say they’ve yet to discover whether just hide the strike or KillDisk’s occupation was to knock out power.

Cybercriminals have been using variations of BlackEnergy since 2007.