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In May 2023, the FBI and international partners used a court-authorized operation called MEDUSA to disable identified infections of Snake, a covert cyberespionage implant attributed by U.S. agencies to a unit within Russia’s FSB Center 16. The FBI’s PERSEUS tool sent commands that caused Snake to overwrite vital components of itself. The operation disrupted the malware on targeted computers; it did not patch those systems or investigate every other way attackers might have retained access.
What is Snake malware?
Snake is a cyberespionage implant and network that U.S. agencies attribute to a unit within Russia’s Federal Security Service (FSB) Center 16. The agencies described it as a tool for long-term intelligence collection, not ransomware. DOJ said the unit had used versions of Snake for nearly 20 years; the joint advisory traces its development under the name Uroburos to late 2003. The May 9, 2023 joint advisory calls it the most sophisticated cyberespionage tool designed and used by that Center 16 unit. That is the agencies’ assessment, not an independent ranking.
The advisory describes operators and infrastructure associated with the broader Turla toolset. DOJ said court documents refer to the FSB unit as Turla. These are U.S. government attributions.
How did Snake work?
Snake did not rely on a single obvious connection between an infected computer and its operators. Infected machines formed a covert peer-to-peer network: some acted as relays, routing disguised traffic between Snake implants and targets. This design could obscure the path of communications.
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- Concealed communications: Snake used custom protocols with encryption and fragmentation.
- Multiple platforms: The advisory describes interoperable implants and modular components observed on Windows, macOS, and Linux.
- Intelligence collection: Reported targets included government networks, research facilities, journalists, and others of interest. The advisory describes one victim in a NATO country from whom sensitive international-relations documents and diplomatic communications were exfiltrated.
U.S. victims identified in the advisory spanned education, small business, media, government facilities, financial services, critical manufacturing, and communications. Those sectors describe victims found in the investigation; they do not mean every organization in each sector was targeted or compromised.
How widespread was Snake?
The public figures describe identified infrastructure and systems, not a definitive count of every infected device worldwide.
| Source and year | Reported scope | What the figure describes |
|---|---|---|
| CISA, FBI, NSA, U.S. Cyber Command Cyber National Mission Force, and Five Eyes partners, 2023 | More than 50 countries | Identified Snake infrastructure across the Americas, Europe, Africa, Asia, and Australia. |
| U.S. Department of Justice, 2023 | Hundreds of computer systems in at least 50 countries | Systems and countries associated with Snake operations, as described in DOJ’s announcement. |
What was Operation MEDUSA?
Operation MEDUSA was the FBI-led disruption announced by the U.S. Department of Justice on May 9, 2023. PERSEUS was the FBI-created tool used in the operation; Snake was the implant being disabled. The names refer to different things.
- The FBI analyzed Snake and its network, developing the ability to decode its communications and communicate with implants using their custom protocol.
- PERSEUS established a session with an identified implant and sent built-in commands.
- Those commands caused Snake to terminate and overwrite vital components of itself. The operation’s affidavit described the intended technique as affecting the implant without affecting legitimate applications or files.
- In the United States, the FBI conducted the remote action under a search warrant authorizing access to identified compromised computers. Foreign authorities worked with the FBI on notifications and remediation in their own jurisdictions.
DOJ described the operation as disabling Snake on compromised computers. It was a targeted action against systems identified as infected, not a general-purpose tool for cleaning arbitrary networks.
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What did the takedown leave for organizations to do?
Disabling Snake did not establish that a victim network was otherwise secure. DOJ explicitly said MEDUSA did not patch vulnerabilities or search for and remove other malware or hacking tools that might have been placed on affected networks. The joint advisory also says Turla often deployed a keylogger with Snake and warns that stolen credentials could support fraudulent re-access.
Organizations that may have been affected should use the joint CISA advisory for technical context and current operational guidance, then address the wider incident rather than treating the disruption as a complete remediation:
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- Investigate affected systems and hunt for related activity or other attacker tools.
- Patch exposed systems and vulnerabilities; PERSEUS did not do this.
- Assess potential credential theft and take appropriate steps to prevent stolen credentials from being reused.
- Use current agency advisories and indicators for operational decisions. The public announcement and advisory document the 2023 operation; they do not establish that every historical infection worldwide was found or that no later Snake-related activity occurred.
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