A group of Russian hackers known as Energetic Bear are systematically targeting hundreds of Western energy companies with malware that could disrupt power supplies, it has been claimed.
Private cybersecurity researchers say the primary motive behind the attacks appears to be industrial espionage, but the software also allows the hackers to seize control of control systems from afar.
This could allow the culprits to sabotage facilities or disrupt power supplies to homes and businesses.
The attacks have affected more than 1,000 organisations in more than 84 countries, according to researchers at CrowdStrike, and were first discovered in August 2012.
The California-based company has since observed unusually sophisticated attacks on healthcare bodies, defence contractors and government agencies.
Now computer security company Symantec has revealed that the hacking group - which it nicknames Dragonfly - has remote-control capability over some power systems.
A statement from Symantec said: "Among the targets of Dragonfly were energy grid operators, major electricity generation firms, petroleum pipeline operators, and energy industry industrial equipment providers.
"The majority of the victims were located in the United States, Spain, France, Italy, Germany, Turkey, and Poland."
It is understood the hackers covered their tracks by using advanced encryption techniques.
Finnish security firm F-Secure has said that in the past six months the group has become more sophisticated and aggressive.
The campaign is similar to alleged cyberwarfare attacks mounted by the US and Israel that used a virus called Stuxnet to damage the Iranian nuclear industry in July 2010.