Overwritten data

When data has been physically overwritten on a hard disk drive it is generally assumed that the previous data is no longer possible to recover. In 1996, Peter Gutmann, a computer scientist, presented a paper that suggested overwritten data could be recovered through the use of magnetic force microscope. In 2001, he presented another paper on a similar topic. Substantial criticism has followed, primarily dealing with the lack of any concrete examples of significant amounts of overwritten data being recovered.Although Gutmann's theory may be correct, there is no practical evidence that overwritten data can be recovered. Moreover, there are good reasons to think that it cannot. To guard against this type of data recovery, Gutmann and Colin Plumb designed a method of irreversibly scrubbing data, known as the Gutmann method and used by several disk-scrubbing software packages.