Do Not Track

The Do Not Track (DNT) header is the proposed HTTP header field DNT that requests that a web application disable either its tracking or cross-site user tracking (the ambiguity remains unresolved) of an individual user. The Do Not Track header was originally proposed in 2009 by researchers Christopher Soghoian, Sid Stamm, and Dan Kaminsky. Efforts to standardize Do Not Track by the W3C in the Tracking Preference Expression (DNT) Working Group are currently advanced at Candidate Recommendation status (as of 20 August 2015).

In December 2010, Microsoft announced support for the DNT mechanism in its Internet Explorer 9 web browser. Mozilla's Firefox became the first browser to implement the feature, while Internet Explorer, Apple's Safari,Opera and Google Chrome all later added support.

The header field name is DNT and it currently accepts three values: 1 in case the user does not want to be tracked (opt out), 0 in case the user consents to being tracked (opt in), or null (no header sent) if the user has not expressed a preference. The default behavior required by the standard is not to send the header unless the user enables the setting via their browser or their choice is implied by use of that specific browser.

In 2007, several consumer advocacy groups asked the U.S. Federal Trade Commission to create a Do Not Track list for online advertising. The proposal would have required that online advertisers submit their information to the FTC, which would compile a machine-readable list of the domain names used by those companies to place cookies or otherwise track consumers.

In July 2009, researchers Christopher Soghoian and Sid Stamm created a prototype add-on for the Firefox web browser, implementing support for the Do Not Track header. Stamm was, at the time, a privacy engineer at Mozilla, while Soghoian soon afterward started working at the FTC. One year later, during a U.S. Senate privacy hearing, FTC Chairman Jon Leibowitz told the Senate Commerce Committee that the commission was exploring the idea of proposing a "do-not-track" list.

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