Did you know deleted files from your hard drive can easily be recovered, even if you empty the recycle bin, You think they are gone, but they can easily be restored using data recovery tools.
Here is a quick guide on how to permanently delete a file or wiping out a hard disk on Windows and Linux
On Windows you need to download a file shredder program, if you have "Spybot Search and Destroy" on your PC you probably all ready have a file shredder installed, you can just goto Start > Programs > Spybot Search and Destroy you should see File Shredder under Spybot Seacrh and Destroy sub menu.
Click on it to start it up, then Add the files you wanted to be Shred, indicate how many times you want it to overwrite (pass through the area on your hard disk), at least 32 times is recommended, wait for it to finish then your done.
On Linux you can use Shred, a command line Linux tool to shred files or hard disk
If you want to Shred or permanently delete a file on your hard disk the command and see what shred is doing use the -v option
shred -uv yourfilehere
if you want to shred an entire hard disk you can use the command below while attaching the hard disk that you want to erase as a second disk, if you have only one hard disk and you want to shred that disk, you will have to boot from a Live CD Linux like Ubuntu and use the command below which will overwrite the disk 32 times for more details on shred do "man shred"
shred -vf -n 32 /dev/yourhardisk
Note: Shredding entire disk take a lot of time, also after shredding you will need to rebuild your partition table and format your hard disk.
That's it for now.