Delete confidential files permanently. Why? Because someone with a recovery software can easily restore deleted files. To permanently erase files and prevent confidential files getting into wrong hands, Microsoft offers a free command line utility – SDelete (Secure Delete) – this overwrites all the space occupied by the files you delete to prevent data recovery. This command line utility is part of the Sysinternals Suite.
P.S: files can be recovered even if you delete them with ‘Shift+Delete’ or you Empty the Recycle Bin, so yes… secure delete confidential files when there is a little chance that someone might recover them back