You may receive a notice similar to the following when using the Transmission app on your Mac. The notice may ask you to upgrade to either version 2.91 or 2.92.

A new version of Transmission is available!

Transmission 2.91 is now available—you have 2.90. Would you like to download it now?

Release Notes:

Everyone running 2.90 on OS X should immediately upgrade to 2.91 (or delete this app), as they may have downloaded a malware-infected file.

Using "Activity Monitor" preinstalled in OS X, check whether any process named "kernel_service" is running. If so, double check the process, choose the "Open Files and Ports" and check whether there is a file name like "/Users//Library/kernel_service". If so, the process is KeRanger's main process. We suggest terminating it with "Quit -> Force Quit".

Some copies of version 2.90 of Transmission were infected with ransomware called KeRanger. The developers of Transmission sent out the notification to users of its software to urge them to upgrade to ensure they are not running an infected version of the software.

Use the integrated buttons to upgrade to the newest version of Transmission (currently 3.00).