Hi
Problem is most word processors, picture editors etc make back up copies which are deleted when file is saved.
If auto save in on there may be regular backups and series of deleted files all waiting to be recovered.
If you destroy the lattest visible copy of file there are still copies waiting to be undeleted
This ignores recycle bin which makes undeleting files easier
Heidi Eraser has two functions
1) destroy specific files
2) over write free (un used) space on hard drive so files can not be un deleted
I believe CCleaner has a similar feature to over write free space
If you want to clean up a usb drive then provided you have Win Vista or later a Format and unticking 'quick format' overwrites all the space on drive
regards...