The only way to ensure that deleted files, as well as files that you encrypt with EFS, are safe from recovery is to use a secure delete application. Secure delete applications overwrite a deleted file’s on-disk data using techiques that are shown to make disk data unrecoverable, even using recovery technology that can read patterns in magnetic media that reveal weakly deleted files. SDelete (Secure Delete) is such an application. You can use SDelete both to securely delete existing files, as well as to securely erase any file data that exists in the unallocated portions of a disk (including files that you have already deleted or encrypted). SDelete implements the Department of Defense clearing and sanitizing standard DOD 5220.22-M, to give you confidence that once deleted with SDelete, your file data is gone forever. Note that SDelete securely deletes file data, but not file names located in free disk space.
SDelete is a command line utility that takes a number of options. In any given use, it allows you to delete one or more files and/or directories, or to cleanse the free space on a logical disk. SDelete accepts wild card characters as part of the directory or file specifier.
Usage: sdelete [-p passes] [-s] [-q] <file or directory> …
sdelete [-p passes] [-z|-c] [drive letter] …
-a Remove Read-Only attribute.
-c Clean free space.
-p passes Specifies number of overwrite passes (default is 1).
-q Don’t print errors (Quiet).
-s or -r Recurse subdirectories.
-z Zero free space (good for virtual disk optimization).