OS X Mountain Lion: Encrypt disks or removable media
Using removable media, such as CDs, DVDs, removable disks, or memory cards, has become a popular way to transport information. However, if the removable media is lost or stolen, someone else can access its data by mounting the media on a computer.
If you want to keep private or confidential information secure on removable media, you need to encrypt the information on it.
- In the Finder, open a window, press the Control key, and then click the disk you want to encrypt in the sidebar.
- Choose Encrypt [Your disk name] from the shortcut menu.
Choosing the startup disk turns on FileVault for your system.
It may take some time to encrypt your disk, depending on how much information you have on it. However, you can use the computer as usual while the disk is being encrypted.
To learn more about encryption, see this help topic: