Update: Version 2.92 of Transmission has now been released. This claims to actively remove the ‘KeyRanger’ malware files from the infected Mac.

OS X users have today been hit with the first known case of Mac ‘ransomware’ malware, found in the Transmission BitTorrent client released last week. Infected versions of the app include ‘KeyRanger’ malware that will maliciously encrypt the user’s hard drive after three days of being installed. The malware then asks for payment to allow the user to decrypt the disk and access their data — the ‘ransom’.

As reported by Palo Alto Networks, Apple has already taken steps to curb the spread of the malware through its Gatekeeper security system. This means the infected version of Transmission will no longer install, but it does not help those who have already been affected. Transmission is urgently recommending people upgrade to the latest version of its software, 2.91.