When you delete a file, Windows removes the index for the file and prevents the operating system from accessing the file’s contents. However, an attacker with direct access to the disk can still recover the file’s contents until it has been overwritten by another file—which might never happen. Similarly, files that have been EFS-encrypted leave behind the unencrypted contents of the file on the disk.
With the SDelete tool, which you can download for free, you can overwrite the contents of free space on your disk to prevent deleted or encrypted files from being recovered.
To use SDelete to overwrite deleted files on the C drive, run the following command:
sdelete -z C: SDelete - Secure Delete v1.51 Copyright (C) 1999-2005 Mark Russinovich Sysinternals - www.sysinternals.com SDelete is set for 1 pass. Free space cleaned on C: