You need to get a disk-wiping program, preferably one that meets the U.S. Department of Defense’s Media Sanitation Guidelines

You need to get a disk-wiping program, preferably one that meets the U.S. Department of Defense’s Media Sanitation Guidelines, and you need to set aside a few hours. What a good disk-wiping program will do is write all sorts of data on your hard disk multiple times, effectively obscuring your original data with newer, nonpersonal stuff. This takes some time, so don’t procrastinate and leave it to the morning of your planned recycling run. Mac users looking for disk-wiping programs can use Mireth Technology’s ShredIt X ($25). Article: Recycle your old tech gear