A download site surreptitiously served Linux users malware that stole passwords and other sensitive information for more than three years until it finally went quiet, researchers said on Tuesday.

The site, freedownloadmanager[.]org, offered a benign version of a Linux offering known as the Free Download Manager. Starting in 2020, the same domain at times redirected users to the domain deb.fdmpkg[.]org, which served a malicious version of the app. The version available on the malicious domain contained a script that downloaded two executable files to the /var/tmp/crond and /var/tmp/bs file paths. The script then used the cron job scheduler to cause the file at /var/tmp/crond to launch every 10 minutes. With that, devices that had installed the booby-trapped version of Free Download Manager were permanently backdoored.

After accessing an IP address for the malicious domain, the backdoor launched a reverse shell that allowed the attackers to remotely control the infected device. Researchers from Kaspersky, the security firm that discovered the malware, then ran the backdoor on a lab device to observe how it behaved.