You may have confidential data on your hard drive in spaces where data may have been stored temporarily. You may also have deleted files by using the Windows Recycle Bin and then emptying it. While you are still using your local hard drive, there may be confidential information available in these unoccupied spaces.
Wiping the logical drive's deleted data does not delete existing files and folders. It processes all unoccupied drive space so that recovery of previously deleted files becomes impossible. Installed applications and existing data are not touched by this process.
When you wipe unoccupied drive space, the process is run from the bootable CD/DVD operating system. As a result, the wipe or erase process uses an operating system that is outside the local hard drive and is not impeded by Windows system caching. This means that deleted Windows system records can be wiped clean.
KillDisk wipes unused data residue from file slack space, unused sectors, and unused space in MTF records or directory records.
Wiping drive space can take a long time, so do this when the system is not being otherwise utilized. For example, this can be done overnight.