Deleting files from Windows systems (even using the shift- delete option) will not make them disappear from the hard drive. They are just erased from Windows indexes but they still exist, and any recovery program can retrieve them. Even after the disk has been formatted, the data is still recoverable.
Hard Disk Scrubber is an application that permanently deletes files from the system by overwriting the space they previously occupied. The program offers five types of overwriting, called scrubs.
Normal overwriting mode will write a string of ones and zeros using a single pass and a random pattern. The Heavy type uses three passes with ones and zeros, and some random passes. Super overwriting type will pass five times, using ones and zeros combinations and checkboard beginning with one and zero, then random passes. The Ultra type or scrub is made accordingly to US Department of Defense security standards, and repeats three times the following operations: double overwrite, an overwrite with 1's compliment, a random overwrite, and a verification. The last type is a custom one, and can be set using a script.
The overwriting process can have various system priorities assigned, to determine the system's resources usage.
Hard Disk Scrubber works under Windows 2000 SP2 or greater, Windows 2000 Server, Windows X, Windows Vista, and Windows 7.