Page 330 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Purging Purging is a more intense form of clearing that prepares
media for reuse in less secure environments. It provides a level of

assurance that the original data is not recoverable using any known
methods. A purging process will repeat the clearing process multiple
times and may combine it with another method such as degaussing to
completely remove the data. Even though purging is intended to
remove all data remnants, it isn’t always trusted. For example, the U.S.
government doesn’t consider any purging method acceptable to purge
top secret data. Media labeled top secret will always remain top secret

until it is destroyed.

Degaussing A degausser creates a strong magnetic field that erases
data on some media in a process called degaussing. Technicians
commonly use degaussing methods to remove data from magnetic
tapes with the goal of returning the tape to its original state. It is
possible to degauss hard disks, but we don’t recommend it.
Degaussing a hard disk will normally destroy the electronics used to

access the data. However, you won’t have any assurance that all of the
data on the disk has actually been destroyed. Someone could open the
drive in a clean room and install the platters on a different drive to
read the data. Degaussing does not affect optical CDs, DVDs, or SSDs.

Destruction Destruction is the final stage in the lifecycle of media
and is the most secure method of sanitizing media. When destroying

media it’s important to ensure that the media cannot be reused or
repaired and that data cannot be extracted from the destroyed media.
Methods of destruction include incineration, crushing, shredding,
disintegration, and dissolving using caustic or acidic chemicals. Some
organizations remove the platters in highly classified disk drives and
destroy them separately.

When organizations donate or sell used computer

equipment, they often remove and destroy storage devices that
hold sensitive data rather than attempting to purge them. This

eliminates the risk that the purging process wasn’t complete, thus
resulting in a loss of confidentiality.