Page 327 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

the wrong hands and result in unauthorized disclosure. Highly
classified data requires different steps to destroy it than data classified

at a lower level. An organization’s security policy or data policy should
define the acceptable methods of destroying data based on the data’s
classification. For example, an organization may require the complete
destruction of media holding highly classified data, but allow
personnel to use software tools to overwrite data files classified at a
lower level.

NIST SP 800-88r1, “Guidelines for Media Sanitization,” provides
comprehensive details on different sanitization methods. Sanitization
methods (such as clearing, purging, and destroying) ensure that data
cannot be recovered by any means. When a computer is disposed of,
sanitization includes ensuring that all nonvolatile memory has been
removed or destroyed; the system doesn’t have compact discs
(CDs)/digital versatile discs (DVDs) in any drive; and internal drives
(hard drives and solid-state drives (SSDs) have been sanitized,

removed, and/or destroyed. Sanitization can refer to the destruction of
media or using a trusted method to purge classified data from the
media without destroying it.

Eliminating Data Remanence

Data remanence is the data that remains on media after the data was
supposedly erased. It typically refers to data on a hard drive as
residual magnetic flux. Using system tools to delete data generally

leaves much of the data remaining on the media, and widely available
tools can easily undelete it. Even when you use sophisticated tools to
overwrite the media, traces of the original data may remain as less
perceptible magnetic fields. This is similar to a ghost image that can
remain on some TV and computer monitors if the same data is
displayed for long periods of time. Forensics experts and attackers

have tools they can use to retrieve this data even after it has been
supposedly overwritten.

One way to remove data remanence is with a degausser. A degausser
generates a heavy magnetic field, which realigns the magnetic fields in
magnetic media such as traditional hard drives, magnetic tape, and
floppy disk drives. Degaussers using power will reliably rewrite these