disk scrubbing
Refers to a software utility used to completely wipe-out hard disk drives. This type of utility can usually overwrite single files, unused space on a disk, or a whole disk drive, using a series of algorithms to make it highly unlikely that anyone could ever retrieve the original data from the disk.
Also see "Are Deleted Files Completely Erased?" in the "Did You Know . . . ?" section of Webopedia.


