First Known OS X Ransomware Found in Transmission BitTorrent Client

Users of BitTorrent client app Transmission became the first reported victims of Mac ransomware this week. Users who downloaded infected versions of the app also received “KeRanger” malware, Reuters says, nefarious software that would encrypt a user’s hard drive three days after being installed and demand payment to unlock the data.

Ransomware has hit headlines in recent months but Transmission’s infection marks the first time a fully functional form of this specific type of malware has been reported on OS X.

Palo Alto Networks notes that only one other piece of ransomware for Apple’s desktop OS, an unfinished bit of software known as FileCoder, spotted by Kaspersky Labs in 2014 and never widely deployed.

Apple moved swiftly to control the ransomware after it was first informed about the issue on March 4th, revoking the certificate it uses, and making it so the infected app will no longer install.

The Transmission Project, which makes the open-source app, has also released a new, clean version of its software, and has recommended users upgrade as soon as possible. If you were infected by the ransomeware, security experts suggest restoring your Mac from a system backup that was completed before you were infected.