Russian hackers broke into the networks of some of the biggest energy companies in the US last year, fresh reports have suggested.
According to the The Wall Street Journal, the cyber attacks were on such a scale that they might have even been responsible for causing blackouts.
Citing officials at the Department of Homeland Security (DHS), the hacks were first detected in the spring of 2016 and continued throughout 2017, carried out by hackers who worked for a Russian state-sponsored group previously known as Dragonfly or Energetic Bear.
DHS officials did not immediately respond to request for comment but said the hacking campaign will most likely to continue.
The report also suggests there might even be a some US companies that were compromised and don't know about it because the hackers used the identities of actual employees to enter the utility networks, which made efforts to detect the intrusions even more difficult.
However, the journal said Russia denies targeting "critical infrastructure" in the US.
The news comes after the DHS and the FBI released a report earlier this year accusing Russian hacking of attempting to break-in to US government organisation networks and even trying to penetrate US infrastructure, including the power sector.
The attacks included hacks in energy, nuclear, commercial, water, and aviation sectors, with the agencies claiming that they have been continuing for at least the past year.
The DHS report described the attacks as "a multi-stage intrusion campaign by Russian government cyber actors" and claims that those behind the attacks are targeting two types of entities.
The first group was organisations linked to their ultimate targets, such as third-party suppliers with networks that may be less secure than those of their main targets. Then, after gaining a foothold on their networks and gathering useful information, they apparently conducted malware-bearing phishing campaigns on their main targets.
However, the report didn't say what sort of impact the attacks may have had on the US infrastructure organisations.
Cotton seedling freezes to death as Chang'e-4 shuts down for the Moon's 14-day lunar night
Fortnite easily out-earns PUBG, Assassin's Creed Odyssey and Red Dead Redemption 2 in 2018
Meteor showers as a service will be visible for about 100 kilometres in all directions
Saturn's rings only formed in the past 100 million years, suggests analysis of Cassini space probe data
New findings contradict conventional belief that Saturn's rings were formed along with the planet about 4.5 billion years ago