When desktops or laptops are replaced or become obsolete, they are commonly transferred or disposed of as surplus property. The Problem: "Delete" or "Format" is NOT Enough!
Non-technical users may assume that simply "deleting" the files on a system's hard drive (or "formatting" that disk) may be sufficient to destroy the contents of that drive or disk. Unfortunately, that is not the case: simply "deleting" files or "formatting" a hard drive will not be enough to definitively destroy information formerly stored on that drive. In fact, deleted files or information on a formatted drive will most likely still be recoverable--which means that private or sensitive data is vulnerable to inappropriate disclosure if special additional measures aren't taken.
For example, a recent article (see "Dumped hard drives tell all" ) reported that 113 of 200 drives purchased on eBay as part of a security vendor's study on disk sanitization still contained recoverable data, including data that in some cases appeared to be confidential or quite personal in nature. If you are transferring or surplusing a computer system, you must sanitize that machine before transferring or otherwise disposing of that system.

There are two common approaches to sanitizing disks in a system. The first is to employ a software disk "wiping" or "overwriting" utility. The other is to physically destroy the hard disk. For example, software disk-wiping utilities obviously cannot sanitize disconnected and forgotten internal hard drives, or hard drives that have physically failed. Likewise, disk wiping is not government-approved for sanitizing particularly sensitive information because a particularly determined adversary might be able to recover inter-track residual data.

In other cases, using a software disk wiping tool may take far too much time, particularly if you have lots of drives or extra-large drives (remember that disk wiping tools repeatedly overwrite the entire drive, a process that can take hours depending on the number of passes performed, the size of the drive, and the speed of the system).

Hard Drive Destruction. When standard software disk wiping isn't enough, drives will normally be removed from the host computer and then destroyed.