How to securely delete files or erase the whole hard disk

Jephe Wu - http://linuxtechres.blogspot.com

Objective: securely delete files for Windows and Linux or erase the whole hard disk
Environment: Windows and Linux


Steps:
1. delete files only
a. use free GUI open source tools eraser - http://eraser.heidi.ie/
note: When I use version 6.0.7 under Windows vista, it cannot start, saying 'Eraser has  stopped working', you can solve it by deleting C:\Users\Jephe\AppData\Local\Eraser 6\Task List.ersx.

b. use sdelete at http://technet.microsoft.com/en-us/sysinternals/bb897443.aspx

c. use DOS-based tool 'secure erase' at http://cmrr.ucsd.edu/people/Hughes/SecureErase.shtml

d. freeraser - http://www.codyssey.com/products/freeraser.html

e. use shred for Linux


2. erase the whole hard disk
a. use http://www.dban.org ISO CD

b. use free version of Active @ killdisk at http://www.killdisk.com/downloadfree.htm

c. use dd or ddrescue command
dd if=/dev/zero of=/dev/sda