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FBI officials on Tuesday dropped a major bombshell: After spending years monitoring exceptionally stealthy malware that one of the Kremlin’s most advanced hacker units had installed on hundreds of computers around the world, agents unloaded a payload that caused the malware to disable itself.

The counter hack took aim at Snake, the name of a sprawling piece of cross-platform malware that for more than two decades has been in use for espionage and sabotage. Snake is developed and operated by Turla, one of the world’s most sophisticated APTs, short for advanced persistent threats, a term for long-running hacking outfits sponsored by nation states.

Inside jokes, taunts, and mythical dragons

If nation-sponsored hacking was baseball, then Turla would not just be a Major League team—it would be a perennial playoff contender. Researchers from multiple security firms largely agree that Turla was behind breaches of the US Department of Defense in 2008, and more recently the German Foreign Office and France’s military. The group has also been known for unleashing stealthy Linux malware and using satellite-based Internet links to maintain the stealth of its operations.