Disk Utility 12.x: Erase Free Space Options dialog

When you delete files by emptying the Trash, Mac OS X deletes the information used to access the files but doesn’t actually delete the files. With the Erase Free Space Options dialog, you can erase the free space used by deleted files so they can’t be recovered by a disk recovery application. Erasing free disk space does not erase the other files on your disk.

Drag the slider to choose how many times to write over the free space. Writing over the space 3 times meets the U.S. Department of Energy (DoE) standard for securely erasing magnetic media. Writing over the space 7 times meets the U.S. Department of Defense (DoD) 5220-22-M standard.

If you have a lot of free space on your disk, overwriting the free space several times can take a long time. After the process begins, you can interrupt it without harming your data.