From the earliest beginnings of computer usage the issue of how to prevent private or sensitive information from being recovered has been discussed. People used to be careful about putting files of this sort into the recycle bin, then emptying the recycle bin. It has become more apparent now though that is procedure does not prevent the access to any and all information which is or has been stored on the computer at any time in its history.
Another method commonly believed to eradicate private files is the process of defragmentation. Then the experts assured computer users that even defragmentation was not enough to permanently remove information from the computer. In essence the statement has been made that the only truly effective way to permanently destroy the information stored on a hard drive is to completely destroy the drive.
A brief analogy of how the files on a hard drive are arranged might help to understand the difficulty. If you had an enormous warehouse filled with file folders in file cabinets and drawers and you had some bit of information in one of those files that you no longer needed. If you left the material in the file folder yet...