A code connected to Russian cyber-hackers has been found on an American electricity company's computer, in further evidence of "predatory" steps taken by Moscow against the US, officials said yesterday.
The discovery came as Russian diplomats and their families prepared to return to Moscow ahead of a New Year's Day expulsion deadline set by President Barack Obama.
The malicious software, or malware, found in the Burlington Electric Department system in Vermont, was linked to the Russian hacking operation dubbed Grizzly Steppe by US officials and raised fears about the vulnerability of America's electricity grid to cyber attacks.
"This attack shows how rampant Russian hacking is. It's systemic, relentless, predatory," said Peter Welch, a Vermont Democratic congressman.
"They will hack everywhere, even Vermont, in pursuit of opportunities to disrupt our country."
The company said it had been alerted by the government last Thursday night, carried out a scan and found the malware in one laptop not connected to its grid systems. It said it took action to isolate the particular laptop.
The US electricity grid is highly computerised and experts have said disruptions could have disastrous implications for the country's medical and emergency services. The Russians did not actively use the code to damage the company, according to an official who spoke to The Washington Post.
The Kremlin has form when it comes to this type of attack, and also in its targeting of a power facility. In December 2015, a power failure that plunged parts of western Ukraine into the dark, was found to have been caused by a cyber attack. The Russians were accused of causing the blackout, an allegation they have denied.
The development follows a climax of hostilities between Barack Obama and Vladimir Putin, the Russian president.
Last Thursday, the White House ordered the expulsion of 35 Russian suspected spies and imposed sanctions on two Russian intelligence agencies over their involvement in cyber attacks that US intelligence officials say influenced November's presidential election.
Obama also closed down two diplomatic compounds in New York and Maryland. Putin decided not to retaliate with tit-for-tat expulsions of Americans, instead stating that Russia would plans its next steps based on president-elect Donald Trump's policies when he takes office on January 20.
The deadline for the diplomatic expulsions from the US was set to expire at noon local time today, with officials leaving both the Russian consulate in California and its embassy in Washington.
The consulate in San Francisco wrote in a Facebook post that it was saying goodbye to "close to a dozen" staff and their families.
One of the suspected intelligence operatives named for expulsion was the consulate's chef, the post said. It added that three children were among those leaving California and they wouldn't "see Santa or gifts under the fir tree".
The Kremlin announced it was sending its Rossiya Special Flight Squadron aircraft, part of a fleet used by Putin, to bring its officials home.
Last night, boxes were seen being loaded onto a Russian plane at Dulles International airport, just outside Washington.
Putin said in his New Year greeting yesterday that 2016 had been a "difficult" year, but congratulated his country on its accomplishments. The past year "was difficult, but the difficulties we came across united us," he said.
"The main thing is: we believe in ourselves, in our abilities, in our country. We are working, working successfully, and are accomplishing a lot," Putin said, extending a special greeting to those serving and working far from home.