In addition to thoroughly erasing all drive contents, DriveScrubber can now also wipe only the free space of a drive, to delete the remnants of deleted files. With this process, existing files, programs, and the operating system are all left in intact, but any deleted files are unrecoverable. In addition to preparing a computer for sale or donation, this feature allows DriveScrubber to be used for regular security maintenance. Many people believe that when they delete a file, it is permanently erased. It is not. In actuality, the data within the file still remains on the drive, and evidence that the file existed still remains on the drive. This is because of how an operating system saves and deletes files. When a file is deleted, its reference is removed from the file allocation table, but the data that made up the file still remains on the drive. The space occupied by that data is marked as "free space" and is available for overwriting by other newly saved files. Until another file's data is saved over it, the deleted data remains on the drive. Even formatting a drive does not erase data: formatting erases file allocation information and performs other housekeeping functions for data storage, but formatting does NOT erase data. Many people donate or give away their computer, not even realizing that their private information is easily recoverable. Even though you can't see the files (for example, through Windows Explorer), someone using easily available tools can still access files and view their contents. This poses a significant security risk. Since reformatting a drive does not completely erase data, protection from readily available programs that recover data is a necessity.