Do you have personal or sensitive information about yourself or your clients on your Mac? Things such as credit card numbers or passwords? If so, I recommend storing this information in a special kind of file known as an encrypted disk image. I store a list of my own passwords and other sensitive information in such a file on my Mac laptop. This file is always readily available while still being inaccessible to others, even if my laptop were stolen.

Without getting very technical, disk images were invented as a way to make a backup copy of a disk such as a floppy or CD, but other uses have emerged over time. Mac OS X lets you create a blank disk image that can be thought of as an empty folder. Additionally, this file can be encrypted which requires a password when you open it. Thus, in an over-simplified way, you can think of an encrypted disk image as a password-protected folder.

Read my next blog post for step-by-step instructions on how to create and use an encrypted disk image on your Mac. After creating your own secure disk image, copy the files that you want to protect into this disk image. For example, if you keep a list of passwords or other sensitive information in a Word or Excel file, copy this file into the secure disk image. Once you’ve confirmed that this file is inside your disk image, then throw away the original file so it’s no longer sitting unprotected on your Mac’s hard drive.

[Update 2015: Since I wrote this article, password manager applications have become increasingly capable so you could consider one of these. One big advantage offered by password managers, over an encrypted disk image, is that passwords can be synced between Macs, iPhones, iPads and even non-Apple devices. I briefly discuss password managers in my article about strengthening and organizing passwords.]