Hello ruthmh,
When you set up a Time Machine backup, you can elect to encrypt the backup or not. Per the article Keep your Time Machine backup disk for Mac secure - Apple Support:
"Encrypt your backup disk
The best way to keep your backups secure is to encrypt your backup disk. When you switch a Time Capsule or network backup disk from unencrypted to encrypted, your existing backups are erased and new encrypted backup sets are created. When you switch locally connected disks (such as an external disk) to encrypted backups, your data is preserved and encrypted.
If you want to change from unencrypted to encrypted backups, you must remove your backup disk and then set it up again. Follow these steps:
- On your Mac, choose Apple menu
> System Settings > General, then click Time Machine
. - Select your backup disk, click Remove
, then click Forget Destination. - Set up the disk again as an encrypted backup disk.
- For instructions, see Choose a backup disk and set encryption options."
Thanks for using Apple Support Communities!