how to protect MacBook Air against ransomeware

The first line of defence is having lots of backups. Have a Time Machine backup that stays up to date. However, if you don't realize, before Time Machine backs up your computer again, that you've been hacked, it will back up the ransomware as well. So you need another backup (clones are great for this) that you do once a month or so and store in a safe place disconnected from everything. This will prevent it from being held for ransom. You should also create a USB drive with macOS recovery on it so you can shut down the hacked Mac, then boot off the USB drive and erase everything using Disk Utility, then restore from a backup (or copy your clone).

Really that's all a bit paranoid (although backups are a great idea regardless). The weakest link is the human — so ask yourself, "How did the ransom ware get on my PC in the first place?" Read up about phishing attacks and other ways hackers get information they want from people.

If you want a utility that can help alert you to attacks like ransomware, I have heard that Little Flocker (www.littleflocker.com) can help you monitor what's going on. Honestly though, the IT guys at my workplace are always saying that learning a bit about security myself is the best way to keep our data safe. So find the right mix of tools, backups, and learning for yourself, I guess. 🙂

Recommended to read, to prevent installing unwanted software when using your computer, John Galt's Effective defenses against malware and other threats