The Transmission.app installer was infected on March 4th, 2016 and it was found yesterday, so the window is small. If you installed Transmission this weekend, you should read this in detail. The malware waits 3 days before activating, so you have time to remove it. You can otherwise read it in detail because it's interesting. :) New OS X Ransomware KeRanger Infected Transmission BitTorrent Client Installer.