How to Wipe a Hard Drive on a Mac (8 Steps)

Insert your Mac OS X Install or Software Restore CD into your your computer's disk drive, and restart your computer, holding down the 'C' button.
Choose your preferred language and click 'Continue.'
From the menu bar in the Mac OS X Installer window, choose 'Disk Utility.'
On the left-hand side of the Disk Utility window, select your hard drive, and on the right, choose the 'Erase' tab.
From the 'Volume Format' drop-down, choose the 'Mac OS Extended (Journaled)' option.
Type a new name for your hard drive in the 'Name' field and click the 'Security Options' button.
From the Secure Erase Options, choose either the '7-Pass Erase' or the '35-Pass Erase'. Both options will overwrite your data with zeroes several times, and both provide a very high level of security. Click 'OK.'
Click 'Erase,' and confirm that you want to erase the drive. Wait while Disk Utility unmounts, erases and renames your hard drive. This will take several hours if you chose the 7-Pass option, or nearly a day if you chose the 35-Pass option.
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