Time Machine backups are not encrypted by default. You have to opt-in. The configuration is easy if the backup drive is connected via USB/Firewire. If the backup drive is connected by Ethernet/Wi-Fi, the process of setting up Time Machine is more complicated.
Connected via USB/Firewire
Select the option in System Preferences → Time Machine → Select Disk
Connected via Ethernet/Wi-Fi
Basically, you need to manually create an encrypted sparse bundle on the external drive to which you will back up.
- Figure out the name of your computer (and make sure it doesn’t contain spaces) in System Preferences → Sharing
Figure out the address of your main ethernet card. Type in the
Terminal.app located at
ifconfig en1 | grep ether
en0 is Wi-Fi
en0 is Ethernet and
en1 is Wi-Fi
Write down the address for later use.
Disk Utility.app and create a new image:
a) Save As: ComputerName_EthernetAddress (without ":")
b) Name: ComputerName
c) Size: Choose a custom size.
d) Format: Mac OSX Extended (Journaled)
e) Encryption: Choose what you prefer. 128-bit is faster
f) Partitions: Single Partition, Apple Partition Map
g) Image Format: sparse bundle disk image
Keychain Access.app and move the password from your personal keychain (login) to the system keychain.
Start to backup!
[source: Mac OSX Lion Secure Backup to Time Capsule with size limit]
I've used this solution for wireless encrypted backups in Lion myself for a while. However, it's quite slow.
Therefore, you should backup less often and allow it enough time to finish. You can use a free tool such as the TimeMachineEditor to perform backups at custom time intervals or calendar events.