Malware called CRASHOVERRIDE or Industroyer was likely to blame for last year’s power grid attack in the Ukraine that left Kiev in the dark for an hour. And that malware represents the most dangerous threat to industrial control systems since Stuxnet.

These revelations come from separate, but related, reports from Dragos and ESET.

Senior Malware Researcher Anton Cherepanov of Slovakian security firm ESET in a blog earlier this week explained that Industroyer is especially dangerous given its ability to control circuit breakers and electricity substation switches directly using native industrial communication protocols. Those protocols have been in use since before the Internet became commercialized, and predate control systems being connected to the outside world. So security wasn’t a consideration at the time they were designed and put into service.

“That means that the attackers didn’t need to be looking for protocol vulnerabilities,” Cherepanov explained, “all they needed was to teach the malware ‘to speak’ those protocols.”

The ability to speak that language apparently enabled Industroyer to turn off remote terminal units controlling the power system in the Ukraine on Dec. 17, 2016. According to The Hill, it’s believed that Russia is to blame for the attack.

Industroyer reportedly can be used to alter settings, shut down systems, and wipe files. It can be used on various kinds of industrial control systems. And it contains specific attacks for one type of Siemens system.

That said, Robert Lee of Dragos in a blog earlier this week noted that the electric grid is extremely reliable and that, because of that fact, any outages it might suffer would last hours or days as opposed to weeks or months. That said, Lee commented that “CRASHOVERRIDE represents alarming tradecraft and the ability to disrupt operations….”

Lee added that ESET on June 8 called on Dragos to validate its findings to reporters covering the new revelations discussed above. “Dragos was able to confirm much of ESET's analysis and leveraged the digital hashes to find other undisclosed samples and connections to a group we are tracking internally as ELECTRUM,” Lee said. (ELECTRUM is the adversary group behind the 2016 attack of the Ukraine electric grid, Lee explained.)

As for the Stuxnet malware referenced above, that was used by the U.S. and Israel to sabotage the Iranian nuclear arms program.