Exam CISSP Topic 2 Question 580 Discussion

Degaussing is recommended as the best method for purging most
magnetic mediA. Degaussing is a process whereby the magnetic
media is erased, i.e., returned to its initial virgin statE. Erasure via degaussing may be accomplished in two ways:
In AC erasure, the media is degaussed by applying an alternating
field that is reduced in amplitude over time from an initial high
value (i.e., AC-powered)
In DC erasure, the media is saturated by applying a unidirectional
field (i.e., DC-powered or by employing a permanent magnet)
Another point about degaussing: Degaussed magnetic hard drives
will generally require restoration of factory-installed timing tracks,
so data purging is recommendeD. Also, physical destruction of
CDROM or WORM media is required.
*Answer " Overwriting the media with new application data" is not recommended because the application may not completely overwrite the old data properly, and strict configuration controls must be in place on both the operating system and the software itselF. Also, bad sectors on the media may not permit the software to overwrite old data properly. To satisfy the DoD clearing requirement, it is sufficient to write any character to all data locations in question (purging).
To purge the media, the DoD requires overwriting with a pattern,
then its complement, and finally with another pattern; e.g., overwrite
first with 0011 0101, followed by 1100 1010, then 1001 0111. The number of times an overwrite must be accomplished depends on the storage media, sometimes on its sensitivity, and sometimes on differing DoD component requirements, but seven times is often recommended.
*Answer "Applying a concentration of hydriodic acid (55% to 58% solution) to the gamma ferric oxide disk surface" is a rarely used method of media destruction, and acid solutions should be used in a well-ventilated area only by qualified personnel.
*Answer "Making sure the disk is re-circulated as quickly as possible to prevent object reuse" is wrong. Source: NCSC-TG-025 A Guide to Understanding
Data Remanence in Automated Information Systems.