By Justin Pot, HowToGeek.com, May 9, 2017
Encrypt Your Current Backups
You encrypt your Mac’s system drive like you should: if your computer is stolen, your data is safe from prying eyes. But on your desk, right next to your Mac, is a carbon copy of everything on your hard drive: your Time Machine backup. Wouldn’t anyone who grabbed that drive have access to all the same information?
Yes they would, which is why it’s important to encrypt your Time Machine drive. There are two ways to do this, and both are relatively straightforward. You can retroactively encrypt your existing Time Machine backup, which allows you to keep your old backups. The downside: this retroactive encryption can take a long time, which is why you might want to simply create an encrypted partition using Disk Utility and back up to that. Let’s go over both options.