Error displayed after the keychain was encrypted by the ransomware.

From Malwarebytes.

Screenshot of encryption message posted to RUTracker forum.

From Malwarebytes,

Last week, Malwarebytes announced the discovery of new ransomware affecting Apple Computers. “OSX.ThiefQuest” fna “EvilQuest” has been associated with apparent not-too-legit downloads for “Little Snitch,” “Mixed in Key 8,” and “Ableton Live” According to Malwarebytes, the ransomware is likely to show up in other software installers as well.

OSX.ThiefQuest, typical of many ransomware programs, locks you out of your computer’s files and demands payment.

There are steps to consider before, during, and after any malware attack.

THINGS TO DO BEFORE YOUR COMPUTER IS ATTACKED (PREVENTATIVE MEASURES)

Install Anti-Virus Program: Regardless of your operating system, Windows or Mac, you should be running an anti-virus program in the background. Yes, it does take some of your system resources to run it in the background. But, if you don’t have a clean working system, it won’t matter how “fast” it’s running, especially if it’s not running at all!
Be wary of what you install: Just because its the named program you want, make sure its the actual software you want! Ransomeware will attempt to trick you with ever so subtle changes in the name, the source webpage address, or even the contents in the installation process. If it doesn’t look right, feel right or seem too good to be true, it probably isn’t.

Back up, Back up, Back up - see my three earlier posts on the topic (especially the third link)!

THINGS TO DO IF YOU ARE ATTACKED

Run an anti-virus program on your computer. Some anti-virus programs offer a basic anti-virus scanner and remover for free, e.g., Malwarebytes. I have a paid version always running in the background in case something tries to sneak through.
Run an anti-virus program on all of your connected files, e.g., external hard drives, etc.
If you still can’t get rid of it, erase your hard drive, and reinstall your backups. Sorry! 🙁

THINGS TO DO AFTER YOU ARE ATTACKED.