Nobody who values the files on their computer should be without at least two regularly updated methods for backing them up. External drives are perfect for this. You can plug them into your computer, copy over your precious files, and then stick the drives somewhere safe and, ideally, not near your computer in order to maximize the chances that a disaster (fire, burglary, etc.) won’t claim your computer and backups all at once.

The external drive’s portability is ideal for this, but it has a downside. It’s prone to being misplaced, lost, or even stolen if you leave it unwatched for too long in a public place. Then whoever has your drive has your files too. Work data, tax info, family photos. The idea of a stranger having access to all that creeps me out. What you can do, though, is encrypt your entire hard drive so that nobody but you can access anything on the drive without the password.

1. Open the Disk Utility app. You may have to open Apps and then search for it in the search bar. Your connected drive should be shown under “External” in the left sidebar. Click it.
2. Now select Erase on the row of buttons along the top of the Disk Utility window. Before you do, make sure that your external drive doesn’t have any files that aren’t backed up elsewhere, because this step wipes the drive clean in preparation for encryption. If you have files on the drive that exist only there, copy them somewhere else first: to another external drive or a computer. Only then, click Erase.
3. It’ll prompt you to name your drive. Pick something self-explanatory, like “Matt’s Backup Disk 1.” (Just use your own name instead of mine. Or use mine if you like. Fine by me.)
4. When it prompts you to choose a format, pick APFS (Encrypted).
5. Set a password that you’ll remember, and then click Erase. If you write it down, make sure it’s in a place you can find it but nobody else can stumble across it. If you lose the password, there’s no gaining access to the files on the drive. Period. Now just sit back and wait for the task to complete. Then you’re free to begin backing up files to your newly encrypted drive.

Windows 11 comes with BitLocker, which is the program you’ll use to encrypt your drive. The catch is that it’s only available on Windows 11 Pro, Enterprise, and Education.

Unlike macOS’s Disk Utility, BitLocker doesn’t offer an option to erase your whole drive as part of the encryption process. That means you don’t have to back up the files on your drive before encrypting, although I still would because it’s cheap insurance. But that means that preexisting fragmentation and traces of deleted files remain on the drive after encryption. You don’t get that clean slate. It’s a minor hiccup, but a hiccup nonetheless.

1. If your copy of Windows 11 is one of those, open File Explorer, right-click the connected external drive, and click “Turn on BitLocker.”
2. BitLocker will prompt you for a method for unlocking the drive. Choose “Use a Password.” Like with macOS, choose a strong password. It’ll also ask you how you want your Recovery Key, which you can use to gain access to the encrypted drive if you forget or lose your password. I prefer saving it to my Microsoft account over saving the file to my computer.
3. Select “Encrypt Entire Drive,” and then when it asks you to choose the format, pick “XTS-AES.”
4. Hit “Start Encrypting,” and then sit back and wait.

Macs don’t play nicely with BitLocker-encrypted drives, and Windows PCs don’t speak the same language as Mac-encrypted drives. If you plan to connect your external drive to both Macs and Windows computers, use VeraCrypt, a platform-agnostic, third-party alternative that works on Mac, Windows, and Linux. It’s open-source, well vetted, and trustworthy. I’ve used it myself.

1. After you’ve downloaded VeraCrypt, open it and select “Create Volume,” then “Encrypt a Non-System Partition/Drive,” and then “Standard VeraCrypt Volume.” Hit “Select Drive,” and choose your external drive. Select “Create Encrypted Volume and Format It.”
2. This will erase the drive, providing a clean slate without disk fragmentation or remnants of old, deleted files. You know the drill. Make sure any files you have on the disk exist somewhere else, too, or copy them to another place before they’re erased. When it asks you to choose your encryption algorithm, click “AES.”
3. Set a strong password, but don’t forget it or, if you write it down somewhere, lose it. If you do, there’s no getting into the encrypted drive. You’re locked out forever. It’ll ask you to select a format. Choose “exFAT.” That’ll let you connect the drive to Macs, Windows PCs, and Linux systems.
4. VeraCrypt saves the weirdest step for last. It’ll ask you to randomly move your mouse around the window. Just go wild. There are no other instructions other than to go willy-nilly. This is what generates the encryption key. Cool, huh? Do it for 30 seconds or so, and then hit “Format” and wait for the disk to encrypt itself. Now you’ve got an encrypted disk that’ll work with any computer.