Editing Data remanence (section)

==Countermeasures==
{{Main|Data erasure}}

There are three levels commonly recognized for eliminating remnant data:

===Clearing===

'''Clearing''' is the removal of sensitive data from storage devices in such a way that there is assurance that the data may not be reconstructed using normal system functions or software file/data recovery utilities. The data may still be recoverable, but not without special laboratory techniques.<ref name="SP800-88">{{cite web
 | url=http://csrc.nist.gov/publications/drafts/800-88-rev1/sp800_88_r1_draft.pdf
 | title=Special Publication 800-88: Guidelines for Media Sanitization Rev. 1
 | publisher=[[National Institute of Standards and Technology|NIST]]
 |date=6 September 2012|access-date=2014-06-23
}} (542 KB)</ref>

Clearing is typically an administrative protection against accidental disclosure within an organization. For example, before a [[hard drive]] is re-used within an organization, its contents may be cleared to prevent their accidental disclosure to the next user.

===Purging===

'''Purging''' or '''[[Sanitization (classified information)|sanitizing]]''' is the physical rewrite of sensitive data from a system or storage device done with the specific intent of rendering the data unrecoverable at a later time.<ref>{{Cite book|url=https://www.worldcat.org/oclc/759924624|title=Encyclopedia of cryptography and security|date=2011|publisher=Springer|others=Tilborg, Henk C. A. van, 1947-, Jajodia, Sushil.|isbn=978-1-4419-5906-5|edition=[2nd ed.]|location=New York|oclc=759924624}}</ref> Purging, proportional to the sensitivity of the data, is generally done before releasing media beyond control, such as before discarding old media, or moving media to a computer with different security requirements.

===Destruction===
The storage media is made unusable for conventional equipment. Effectiveness of destroying the media varies by medium and method. Depending on recording density of the media, and/or the destruction technique, this may leave data recoverable by laboratory methods. Conversely, destruction using appropriate techniques is the most secure method of preventing retrieval.