If you want to give away or sell your old computer and want to protect your data on the hard drive that you had before, formatting the hard drive and installing Windows again from scratch is not enough! That’s right, even after formatting the hard drive, someone can run some basic data recovery software on it and get back all the personal and private data that you thought was gone.
How do a completely destroy all chances of anyone getting my data off my hard drive after it’s formatted? If the hard drive will not be used again, physically destroying or crushing the hard drive is the best method. If you want to use it again, that option is out of the question. Instead you need software to digitally shred the hard drive with. Here’s some links to various software programs you can get that will do the trick. Of course, the more passes you do on the drive when shredding it, the better; and nothing is 100% full proof besides physically destroying the drive.
http://www.dtransfer.com/products/data-deletion/digital-shredder-premium
http://www.download32.com/digital-document-shredder-i38553.html