April 18, 2013, 2:03 PM — Here's how you can encrypt your iPhone backups in iTunes.
1. Connect your iPhone to your computer.
2. Select your iPhone in the sidebar.
3. Go to Summary tab.
4. Go to Options.
5. Click the checkbox next to "Encrypt iPhone Backup."
For more, see the original article at the link below.
Encrypt your iPhone Backups | OS X Daily