How to Securely Erase a Hard Drive on Your Mac

By Techwalla Contributor

Mac OS X includes a variety of optional features to increase your security. For example, Disk Utility lets you securely erase any hard drive on your Mac. This is helpful if you've decided to recycle or sell an external drive, internal drive or even your Mac. Formatting and deleting files doesn't securely remove them from a hard drive. A person with a recovery program can still find those files later. Overwriting the information is required for real security.

Things You'll Need

  • A Macintosh computer running MacOS X
  • A hard drive that you want to erase
  • A bootable CD or DVD with MacOS X if you plan on erasing your main hard drive

Step 1

Insert your Mac OS X installation disc if the hard drive being erased is your main drive, otherwise proceed to the next step. Restart your Mac and press the "C" key while it starts up to boot from the DVD drive. Select your language and click "Continue."

Step 2

Click the "Disk Utility" option from the "Utilities" menu if you're using an installation disc. If you're still in Mac OS X, open a new Finder window and click the "Utilities" option from the Go menu. Double-click the "Disk Utility" app to start it.

Step 3

Select the disk you want to erase in the list on the left side of the window. Make sure no other applications are using the disk you want to erase. Click the "Erase" tab at the top right side of the window.

Step 4

Click the "Security Options" button. Click one of the security options to use. The "7-Pass Erase" offers reasonable security while not taking as long as the 35-Pass Erase option. Click "OK" after selecting your option.

Step 5

Click the "Erase" button to start the process. Wait until it finishes, then close Disk Utility. If you're using the OS X installation DVD, proceed with installing a clean copy of OS X to sell or donate your Mac.

Tips & Warnings

  • To securely delete a few files in the Trash, open the Trash, click the Finder menu and select the "Secure Empty Trash" option.
  • If your drive is divided into separate partitions (or volumes) make sure you have all of the data (on all its partitions) backed up in case Disk Utility happens to fail.