If you work with highly confidential data, you should know that when you delete a file, it can be restored by certain utilities. Thus, you will want to make sure that when you delete a file, it is gone for good. This is especially the case if you sell your computer to a third party.
One way is to use the Erase Free Space feature in Disk Utility. There are three options: Zero Out, 3-Pass or 7-Pass. Most often, Zero Out (the default) should be sufficient. 3-Pass will do as the name suggests – go through your drive 3 times. Use 7-Pass if you are really paranoid. But be prepared – it will take quite a bit longer than Zero Out or 3-Pass.
To move through the three options, drag the slider bar through the three levels.
To Erase the Free Space on your Hard Drive:
1. Select Go > Utilities from the Finder Menu
2. Double-click “Disk Utility”
3. Choose the drive you want to erase in the left pane
4. Click the Erase tab on top of the window
5. Click the Erase Free Space button
6. To choose Zero Out, ensure that slider is in the leftmost position.
7. To choose 3-Pass, drag the slider to the center of the slider bar.
8. To choose 7-Pass, drag the slider to the far right of the slider bar.
9. Click “Erase Free Space”
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