US intelligence agencies attribute the hack to Russian state actors, but Moscow denies any involvement.
Russia has expressed its alarm after it was reported the United States was planning a series of covert counterattacks on Russian networks, saying such strikes would amount to cybercrimes.
The report by The New York Times on March 7 said the planned US move would be in response to the hacking of SolarWinds software that US officials say was conducted by Russia, something Moscow denies.
“This is alarming information,” Dmitry Peskov, Kremlin spokesman, said on Tuesday. “This would be pure international cybercrime.”
US intelligence agencies in January said Russia was likely behind an enormous hack of government departments and corporations.
In a rare joint statement, the Federal Bureau of Investigations, the National Security Agency and the Cybersecurity and Infrastructure Security Agency said the hacking appeared to be part of “intelligence-gathering” and suggested the evidence so far points to a Russian spying effort rather than an attempt to damage or disrupt government operations.
The agencies said the actor, “likely Russian in origin, is responsible for most or all of the recently discovered, ongoing cyber compromises of both government and non-governmental networks”.
“This is a serious compromise that will require a sustained and dedicated effort to remediate,” the statement said.
Russia has denied involvement in the hack.
Citing officials, the Times reported the US counterattack to the hacking was expected over the next three weeks.
It said a series of clandestine actions were expected across Russian networks that were intended to be evident to President Vladimir Putin and his intelligence services and military but not to the wider world.
US President Joe Biden announced in December last year that cybersecurity would be a priority in his administration.
Under a recent law, Biden must open a cyber-focused office reporting to a new National Cyber Director, who will coordinate the federal government’s vast cyber-capabilities.