The technique described, where an attacker applies a magnetic field to a digital media device to clean it of any previously stored data, is known as disk degaussing. Degaussing is a method used to erase a disk or tape by exposing it to a strong magnetic field, destroying the magnetic data storage mechanism and leaving the device clean of any data. This process is effectively used for wiping digital evidence in a way that makes recovery impossible, serving as a method of anti-forensics. Unlike file wiping utilities or disk cleaning utilities, which overwrite or delete data (potentially leaving traces that can be recovered), degaussing physically alters the storage medium itself, making data recovery unfeasible.References:The ECIH v3 certification program discusses various artifact wiping techniques, including degaussing, as part of understanding anti-forensic methods that attackers use to evade detection and investigation.