Securely erase hard drives on your Mac – OS X Tutorial

Have you ever wondered how technology pros can recover deleted files from a hard drive? It’s because whenever the Trash is emptied on your Mac, OS X deletes the info used to access the file data, but doesn’t actually erase the file itself. To put it simply, OS X puts the data to one side and allows it to be overwritten by other programs and data. That means the data may be overwritten within seconds by the system, or sit on the drive for weeks, months or even permanently if the drive isn’t used again.

Often, for security reasons, it’s necessary to delete this data. Perhaps you’re selling your Mac, or lending it to friends and family for short-term use. It’s easy to delete this ‘free’ space by using Disk Utility, found in the Utilities folder on your Mac. With just one click of the mouse, you can overwrite all of the free space on a hard drive with zeros. Follow us through this tutorial as we explain how it’s done.

Step 1: Get started
Open Disk Utility by searching for it in Spotlight or clicking on the Go  choosing Utilities, then double-clicking on the Disk Utility application.

Step 2: Choose a drive
Click on the main hard drive of your Mac (typically the top drive in the list), then click on the Erase tab in the centre of the screen. You’ll see a button called Erase Free Space below.

Step 3: Choose a security level
Click on this and a window will slide down offering varying security options for erasing deleted data on the drive. See the annotated screenshot on this page for more details about these.

Step 4: Data deleted
The first option, Zero-Out, should be sufficient for most users. Choose this option and click the Erase Free Space button. Disk Utility will now completely erase the deleted data on the drive.

Click on the image below to zoom in and read the annotations.