If you ever think simply format your Hard Drive will erase all the data on your Hard Drive, Sorry you are wrong.
The way data store on the Hard Drive is not like a pencil writing words on a paper and erase the words after. The data that you have stored on the hard drive will not be permanently erased unless there is new data over write on the part that originally contains data on it. Even you do over write some part of the block, you can never guarantee it covered every part of the block, sector on your hard drive. And simply empty the Recycle Bin will not help either. This is how data recovery software worked, it tries to read from the bits that OS think it’s free but haven’t over written yet.
So if you want to disposal or resell your hard drive or computer you might want to consider to securely wipe data on your hard drive before you do anything else.
DBAN (Darik’s Boot and Nuke) is a Linux based bootable utility to permanently remove the data on your hard drive. You can choose how many “pass” you want to run on the hard drive to destroy data. The higher the number of “passes” usually is more secure but at the same time it takes longer to complete as well. The duration also depends on the size of the hard drive as well.
You need to download the ISO file and burn it to your DVD/CD or bootable USB stick.
Download the latest DBAN here