How to Securely Erase Free Space on a Mac Hard Driveby Alexia Petrakos
Once you move documents to the Trash and click on "Empty Trash" your documents are gone for good, right? Not necessarily. Trashing files only tells your computer that the space that file occupied is now available space for new files. That one trashed file may be retrievable for a long time. The only way to truly get rid of your old files is to write over them. Disk Utility in Apple's Mac OSX has a Secure Erase option that writes over all your free space on your hard drive to get rid of all traces of your old files and documents. Here is how to use it.
Launch Disk Utility. It's in your Applications folder under the "Utilities" folder.
Select your Apple Macintosh Computer's hard drive. If you haven't renamed your drive, it should be "Macintosh HD."
Click on the "Erase" tab.
Click the "Erase Free Space..." button.
Select the level of security you want to use when erasing the free space on your Macintosh Computer's hard drive. "Zero Out Deleted Files" is the fastest option and is decent security. It will write over the free space with zeros. "7-Pass Erase of Deleted Files" will write over the free space seven times. This will take longer and offers a higher level of security. "35-Pass Erase of Deleted Files" offers the highest security. It will over-write the free space 35 times and will take the longest. Depending on your hard drive's capacity, this could take several hours to overnight.
Click the "Erase Free Space" button when you've selected your security level.
- check Disk Utility also allows you to securely erase an entire hard drive or removable storage device. This is helpful if you're planning on selling or giving away your storage device.