WipeFS

About

WipeFS erases unused space on hard disks, USB flash drives etc, to prevent the recovery of deleted files.

Any data which still resides in that unused space, albeit marked 'free', can be properly and securely deleted by overwriting it. As you may know, simply deleting a file does not actually delete the content of the file. Instead, the space that file occupied on the disk is simply marked as being 'free', and may exist for a long time until another file is allocated that space (or part of it).