“Is there a way to secure an archive with a password?” asked Macworld reader Alberto Martinez recently. I had a similar question, especially when it comes to making backup CDs of your data. Ideally, you store those backups in a secure place other than your home. But, what if someone else swipes them and uses them? Encryption of your data would be nice in such a case.

According to Macworld author Christopher Breen, “If you select a file in the Finder and choose File: Create Archive, you won’t see an encryption option. But you can use Apple’s Disk Utility to create encrypted disk-image archives. I ran through the process, and eventually ended up with an error message: “no mountable file system”. So, below are revised instructions on how to get around this.

• Launch Disk Utility and choose Images: New: Blank Image
• In the resulting dialog box, enter a name for the newly created disk image. Select a size for the image (i.e. 4.7 GB DVD-R/DVD-RAM), encryption (AES-128) and format (read/write disk image). Click Create.
• You’ll soon see an Authenticate dialog box. Enter and verify a password for the archive. If you don’t want the image to decrypt automatically when opened from your user account, disable the Remember Password (Add To Keychain) option. (In other words, if other people will operate your Mac while logged in to your user account, disable this option so they’ll need the password to decrypt the archive.)
• Click on OK to create the encrypted and compressed archive. Note that you can use these archives only on a Mac—Windows won’t have a clue what to do with them.
• Add your desired files to this disk image. When the copying is completed, eject disk image.