Hacking attacks over the last several months that targeted U.S. energy companies have been able to gain "operational control" over systems, thus threatening blackouts across the U.S., says Symantec.

 The hacker group known as DragonFly 2.0 was able to gain control in at least 20 places, according to the firm.

Wired:

Symantec on Wednesday revealed a new campaign of attacks by a group it is calling Dragonfly 2.0, which it says targeted dozens of energy companies in the spring and summer of this year. In more than 20 cases, Symantec says the hackers successfully gained access to the target companies' networks. And at a handful of US power firms and at least one company in Turkey – none of which Symantec will name – their forensic analysis found that the hackers obtained what they call operational access: control of the interfaces power company engineers use to send actual commands to equipment like circuit breakers, giving them the ability to stop the flow of electricity into US homes and businesses.

"There's a difference between being a step away from conducting sabotage and actually being in a position to conduct sabotage ... being able to flip the switch on power generation," says Eric Chien, a Symantec security analyst. "We're now talking about on-the-ground technical evidence this could happen in the US, and there's nothing left standing in the way except the motivation of some actor out in the world."