Degaussing permanently destroys data on magnetic media by subjecting it to a strong magnetic field that scrambles the alignment holding the bits, leaving the previous contents unrecoverable. It is a standard sanitization method for hard disk drives and magnetic tape reaching end of life or leaving an organization’s control.
The critical limitation trips people up constantly. Degaussing does nothing useful on solid-state drives, flash media, or optical discs, because none of them store data magnetically, and running an SSD through a degausser just wastes time while leaving the data intact. Flash-based media call for cryptographic erasure or physical destruction instead. A strong degausser also renders a traditional drive permanently inoperable, so the device cannot be reused afterward. NIST guidance on media sanitization should drive the method you pick for a given data sensitivity.
How is degaussing tested on the CISSP?
Degaussing sits in Domain 2: Asset Security under data destruction and media sanitization. Candidates must match the right sanitization technique to the media type and to the classification of the data that was stored on it. Expect the exam to contrast degaussing, cryptographic erasure, and physical destruction as options for different media.