We all know that when we delete files or folders in Windows, they’re not actually erased—the space they took up is simply marked as “available for use,” which allows the files to be recoverable (with the right software) until they’re overwritten with new data.
There is a tool which started its journey along with Windows XP and come through Vista, 7 and now 8, that will overwrite all the free space on a hard drive, insuring any files you’ve deleted stay dead.
To get this
Come to Desktop
Press Ctrl + R
Enter “cmd” without quotes and hit enter
Now you are in Command Prompt (You can launch cmd.exe in some more ways)
cipher /w:X where
X is the letter of the drive or partition you want to wipe.
be patient—the process can take a long time if you have a lot of free space. (To wipe a 1GB free space on a memory stick I waited for more then 90 mins)
After this you can not Recover your files using any utility software like Recuva