The introduction leaves Google's Chrome as the only major browser without a do-not-track mechanism.
Apple looks set to include a do-not-track feature in the new version of its popular Safari web browser, which will enable users to specify their desire not to be tracked or targeted by online marketers.
According to a report in the Wall Street Journal, the feature is bundled with the latest test version of Apple's new Lion OS X operating system. Currently only available to developers, the system is slated for public release this summer.
The introduction means a form of do-not-track mechanism is now present in the latest versions of every major U.S. browser besides Google's Chrome, after Microsoft and Mozilla implemented features in their IE9 and Firefox 4 browsers, respectively, earlier this year.
Google has, however, launched a Chrome extension called "Keep My Opt-Outs," which allows users to opt out of being tracked by companies participating in industry self-regulatory efforts lead by the Digital Advertising Alliance. The plugin applies to tracking from those companies alone, though, and represents a slightly different approach to the blanket-based opt-out intended to be achieved through header-based browser mechanisms.
Browser-based opt-outs function by broadcasting a do-not-track header - or signal - as they move across the web. Publishers and third parties such as ad networks can receive and interpret that signal, and in theory refrain from tracking or serving the behavior of that browser.
The mechanism relies, however, on publishers and ad providers agreeing to honor those do-not-track requests. To date the only company to have publicly announced its support for do-not-track is Associated Press, which said it will not track users with its News Registry audience measurement service if they chose to enable the feature.
The Associated Press itself noted that its own sites still carry numerous other third party cookies, though, which highlights the complexity and difficulties surrounding the concept of a browser-based do-not-track feature.
Ultimately, without legislation compelling them to do so, advertisers and technology providers appear unlikely to honor do-not-track headers, as the data gleaned from users' browsers is of great value for ad targeting and conversion-tracking purposes.
UPDATE: This story was edited to include information about Google's Chrome browser extension, "Keep My Opt-Outs."
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Jack Marshall was a staff writer and stats editor for ClickZ News from 2007 until August 2011.
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