Whenever a computer or hard drive is retired from service, it's considered good computer hygiene to erase the hard drive first. The drive might be recycled into another computer, donated to charity or simply sold off -- but whatever its fate, it's good common sense to wipe it clean before putting it into anyone else's hands.
It's often hard to tell what can end up on a given computer, who may see it, and what they might be able to do with it. (In one incident I know of personally, someone who donated a hard drive from his company's discard pool was horrified to find that the drive contained a number of confidential corporate e-mails inadvertently saved as text files.)
Reformatting the hard drive can be a tedious operation, especially if it's the only drive in the system and Windows doesn't allow you to format its own system disk. To make it easy to wipe a system clean, Darik Horn has created a free and open-source tool called DBAN, short for Darik's Boot and Nuke.
DBAN boots from a floppy disk, so it doesn't require a host operating system of any kind and can perform secure and complete disk-wipes of any system with any size hard drive. DBAN is used by, among others, the Department of Energy as a standard data-protection protocol.
DBAN runs from a tiny Linux distribution that contains drivers for all major varieties of hard disk controllers (IDE, SCSI, SATA), so no special drivers are required. It can securely destroy partitions used by all varieties of Windows, MS-DOS and most UNIX-style partitions (such as EXT, UFS and ReiserFS). The number of wipe passes can be user-configured, but there are options within the program for quick-erase (which destroys the partition table and file tables only) or the more secure Canadian RCMP TSSIT OPS-II Wipe; American DoD 5220-22.M Wipe; Gutmann Wipe; and PRNG Stream Wire standards (which use multiple overwrites on the whole disk). The program also has multiple methods of generating random overwrite data, which makes recovery all the more impossible.
The DBAN program natively supports hard disks larger than 137 GB, even when the host system's BIOS doesn't. All of the program's actions can be logged and retained for offline analysis.
Serdar Yegulalp is editor of the Windows Power Users Newsletter. Check it out for the latest advice and musings on the world of Windows network administrators -- and please share your thoughts as well!