What is data remanence and how is it addressed?

Data remanence is the residual representation of data that remains on storage media after deletion or formatting attempts. Simply deleting a file or formatting a drive does not destroy the data because only the reference pointer is removed. Methods to address remanence include overwriting which writes patterns over existing data, degaussing which destroys magnetic fields on magnetic media using a strong electromagnet, and physical destruction through shredding, incineration, or pulverizing. For highly classified data, degaussing or physical destruction is required.