In a rare feat, French police have hijacked and neutralized a massive cryptocurrency mining botnet controlling close to a million infected computers.

The notorious Retadup malware infects computers and starts mining cryptocurrency by sapping power from a computer’s processor. Although the malware was used to generate money, the malware operators easily could have run other malicious code, like spyware or ransomware. The malware also has wormable properties, allowing it to spread from computer to computer.

Since its first appearance, the cryptocurrency mining malware has spread across the world, including the U.S., Russia, and Central and South America.

According to a blog post announcing the bust, security firm Avast confirmed the operation was successful.

The security firm got involved after it discovered a design flaw in the malware’s command and control server. That flaw, if properly exploited, would have “allowed us to remove the malware from its victims’ computers” without pushing any code to victims’ computers, the researchers said.

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