Hackers who hit American utilities this summer had the power to cause blackouts, Symantec says. And yes, most signs point to Russia.

Now, Symantec reports, the group has resumed operations, apparently working since late 2015 to investigate and penetrate energy facilities in at least three countries: the US, Turkey and Switzerland.

“The Dragonfly group appears to be interested in both learning how energy facilities operate and also gaining access to operational systems themselves, to the extent that the group now potentially has the ability to sabotage or gain control of these systems should it decide to do so,” the cybersecurity firm warns.

Dragonfly’s methods are varied, but all its attacks seem to be focused on researching the inner workings of energy firms. It has been seen sending malicious emails with attachments that leak internal network credentials, which are then used to install backdoors on the network allowing the hackers to take control of computers and systems. They’ve also been seen seeding fake flash updates to install the backdoors and carrying out “watering hole” attacks, hacking third-party websites that were likely to be visited by people working in the energy sector.

Cyberattacks can also hit massive oceangoing ships, misdirect GPS signals, and cause mayhem in shipping lanes. Trust in anti-collision protocols falters.