macOS Sierra: Keep your Time Machine backup disk secure
The procedures for keeping your backups secure depend on whether you back up to a Time Capsule or other disk that’s on a network, or to a disk connected directly to your Mac.
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:
Choose Apple menu > System Preferences, then click Time Machine.
Click Select Disk or Add or Remove Backup Disk (if you have multiple backup disks).
Select your backup disk, then click Remove Disk.
Set up the disk again as an encrypted backup disk.
For instructions, see Choose a backup disk and set encryption options.
Safeguard a Time Capsule or other networked disk
If you back up to a disk that’s used by multiple people, such as a Time Capsule or another network disk, be aware that under some conditions other users could have access to your backups.
Only an administrator or other trusted user should have the password for a network disk used for Time Machine backups. Anyone who knows the password can access any data backed up to the disk, regardless of which user owns the data. If the backup is encrypted, it’s safe from users and network administrators that know the network disk password, but don’t know the backup encryption password.
Don’t back up sensitive data to a network disk if you don’t trust the network administrators who control the disk. Instead, select a backup disk that’s under your own control, such as an external disk connected to your Mac.
For security when backing up to a Time Capsule, an administrator can create individual accounts on the Time Capsule. Each account has its own network volume and password. If you back up to your own account volume on a Time Capsule, other users can’t access your backups unless they know your password.
Note: A Time Capsule set up with individual accounts contains a shared volume. Be sure you select your own volume as your backup disk, using the account name and instructions given to you by the administrator. The shared volume is intended only for information that all users can access.
Safeguard a disk connected directly to your Mac
If you back up to an external disk and don’t use disk encryption, any person who gains possession of that disk can read any data backed up to that disk. Be sure to physically safeguard your backup disk so untrusted users don’t have access to it, and store it in a secure location.