Privacy mode or "private browsing", sometimes informally referred to as "porn mode", is a term that refers to privacy features in some web browsers. Historically speaking, web browsers store information such as browsing history, images, videos and text within cache. In contrast, privacy mode can be enabled so that the browser does not store this information for selected browsing sessions. This allows a person to browse the Web without storing local data that could be retrieved at a later date. Privacy mode will also disable the storage of data in cookies and Flash cookies. It is of note that this offers virtually no privacy protection beyond the local level. For example, it is still possible to identify frequented websites by associating the IP address with the user on the server end.
The Mozilla Foundation made a study about the user behavior when the feature is switched on and how long the session lasts. The results were that most sessions last only about 10 minutes, though there are periods where activation increases; usually around 11 a.m. to 2 p.m., 5 p.m., between 9 p.m. and 10 p.m., and a minor peak about an hour or two after midnight.
The earliest reference to the term was in May 2005 and used to discuss the privacy features in the Safari browser bundled with Mac OS X Tiger. The feature has since been adopted in other browsers, and led to popularisation of the term in 2008 by mainstream news outlets and computing websites when discussing beta versions of Internet Explorer 8. However, privacy modes operate as shields because browsers typically do not remove all data from the cache after the session. Plugins, like Silverlight, are able to set cookies that will not be removed after the session. Internet Explorer 8 also contains a feature called InPrivate Subscriptions, an RSS web feed with sites approved for use with InPrivate browsing.
Support in popular browsers 
Privacy mode is known by different names in different browsers:
|April 29, 2005||Safari 2.0||Private Browsing|
|December 11, 2008||Google Chrome 1.0||Incognito|
|March 19, 2009||Internet Explorer 8||InPrivate Browsing|
|June 30, 2009||Mozilla Firefox 3.5||Private Browsing|
|March 2, 2010||Opera 10.50||Private Tab / Private Window|
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- Ulmer, Hamilton (23 August 2010). "Understanding Private Browsing". Blog of Metrics. Mozilla Foundation. Retrieved 24 August 2010.
- Foley, Mary Jo. "Microsoft to roll out more granular 'porn mode' with IE 8". ZDNet. Retrieved 2008-10-04.
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- Xu, Jimson; Nguyen, Tom (30 June 2010). "Private browsing in Flash Player 10.1". Adobe Systems. Retrieved 14 January 2011.
- "Microsoft Announces Availability of Internet Explorer 8" (Press release). Microsoft. 19 March 2009. Retrieved 16 December 2011.
- "Mozilla Cross-Reference mozilla1.9.1". Mozilla Foundation. Retrieved 2009-05-26.
- Mateu, Roberto. "Opera 10.5 pre-alpha for Labs". Opera Software. Retrieved 2009-12-22.