Russia’s GRU has secretly developed and deployed new malware that’s virtually impossible to eradicate, capable of surviving a complete wipe of a target computer’s hard drive, and allows the Kremlin’s hackers to return again and again.

The malware, uncovered by the European security company ESET, works by rewriting the code flashed into a computer’s UEFI chip, a small slab of silicon on the motherboard that controls the boot and reboot process. Its apparent purpose is to maintain access to a high-value target in the event the operating system gets reinstalled or the hard drive replaced—changes that would normally kick out an intruder.

It’s proof that the hackers known as Fancy Bear “may be even more dangerous than previously thought,” company researchers wrote in a blog post. They’re set to present a paper on the malware at the Blue Hat security conference Thursday.

U.S. intelligence agencies have identified Fancy Bear as two units within Russia’s military intelligence directorate, the GRU, and last July Robert Mueller indicted 12 GRU officers for Fancy Bear’s U.S. election interference hacking.

The advanced malware shows the Kremlin’s continued investment in the hacking operation that staged some of the era’s most notorious intrusions, including the 2016 Democratic National Committee hack. The GRU’s hackers have been active for at least 12 years, breaching NATO, Obama’s White House, a French television station, the World Anti-Doping Agency, countless NGOs, and military and civilian agencies in Europe, Central Asia, and the Caucasus. Last year, they targeted targeted Democratic Sen. Claire McCaskill, who’s facing a hotly contested 2018 re-election race.

“There’s been no deterrence to Russian hacking,” said former FBI counterterrorism agent Clint Watts, a research fellow at the Foreign Policy Research Institute. “And as long as there’s no deterrence, they’re not going to stop, and they’re going to get more and more sophisticated.”

As sophisticated as it is, Russia’s new malware works only on PCs with security weaknesses in the existing UEFI configuration. It also isn’t the first code to hide in the UEFI chip. Security researchers have demonstrated the vulnerability with proof-of-concept code in the past, and a 2015 leak showed that commercial spyware manufacturer Hacking Team offered UEFI persistence as an option in one of their products. There’s even evidence that Fancy Bear borrowed snippets of Hacking Team’s code, ESET said.

Last year, a WikiLeaks dump revealed that the CIA used it own malware called “DerStarke” to maintain long-term access to hacked MacOS machines using the same technique.

But until now such an attack has never been spotted in the wild on a victim computer.

The first public whiff of Russia’s new malware emerged last March, when Arbor Networks’ ASERT team reported finding malware designed to look like a component of the theft-recovery app Absolute LoJack.

Absolute LoJack works much like Apple’s Find My iPhone app, allowing laptop owners to attempt to geo-locate a computer after a theft, or to remotely wipe their sensitive files from the missing machine. The hackers copied one piece of the app, a background process that maintains contact with Absolute Software’s server, and changed it to report to Fancy Bear’s command-and-control servers instead.

ESET researchers call the malware LoJax. They suspected they were seeing just one piece of a larger puzzle, and started looking for additional LoJax components in Eastern Europe and the Balkans, where LoJax was popping up on hacked machines alongside better-known Fancy Bear implants like Seduploader, X-Agent, and X-Tunnel.

They found a new component of LoJax designed to access technical details of a computer’s UEFI chip, and surmised that Fancy Bear was moving to the motherboard. Eventually they found the proof in another component called “ReWriter_binary” that actually rewrote vulnerable UEFI chips, replacing the vendor code with Fancy Bear’s code.

Fancy Bear’s UEFI code works as a bodyguard for the the counterfeit LoJack agent. At every reboot, the hacked chip checks to make sure that Windows malware is still present on the hard drive, and if it’s missing, reinstalls it.

The researchers so far have found only one computer with an infected UEFI chip among many with the fake LoJack component, which makes them think the former is only rarely deployed. And by all evidence, the entire project is relatively new.

“The LoJax campaign started at least in early 2017,” said Jean-Ian Boutin, a senior malware researcher at ESET. “ We don’t know exactly when the UEFI rootkit was used for the first time, but our first detection came in early 2018.”

“The GRU is following a developmental model that’s very sophisticated,” said Watts. “They have programmers who seem to be top-notch and they appear to rapidly deploy their cyberweapons not long after they develop them.”

The ESET researchers said the new malware should be taken as a warning. “The LoJax campaign shows that high-value targets are prime candidates for the deployment of rare, even unique threats,” the researchers wrote. “Such targets should always be on the lookout for signs of compromise.”