Google will add support for "Do Not Track" to its Chrome browser by the end of this year.
The move is a reversal for Google, which has resisted supporting the technology that lets users opt out of the online tracking conducted by websites and advertisers.
Google's change of heart came as the White House today pushed a privacy bill of rights and said it would introduce new online privacy legislation in Congress.
Chrome joins other browsers -- Microsoft's Internet Explorer 9 (IE9) and Mozilla's Firefox -- which can already transmit special information with every HTTP page request that tells sites the user does not want to be tracked.
Apple's Safari currently supports Do Not Track, although turning it on requires a user to select "Send Do Not Track HTTP Header" from the "Developer" menu on the browser; Apple will make the setting easier to find in the Privacy section of Safari's Preferences pane this summer when it releases OS X Mountain Lion.
Opera, from the Norwegian browser maker Opera Software, does not support Do Not Track. Two weeks ago, however, Opera launched an experimental build of its desktop browser with support for for the anti-tracking technology.
"This is a great step forward," said Jonathan Mayer, a graduate student in computer science and law at Stanford University. Mayer is one of two principal researchers at Stanford who have been working on the Do Not Track technology that uses information in the HTTP header to universally opt out of all online tracking. "For some time, Google has been the last holdout among the major browsers."
Mayer called out "mad kudos" to the advertising industry for getting behind Do Not Track, but said only part of the problem has been settled.
"As a technology model, Do Not Track is clearly superior to an opt-out mechanism," said Mayer, referring to commitments by Google and other members of the Digital Advertising Alliance (DAA) to support the technology on their websites. "So the technology question is now settled: It's Do Not Track."
What's not settled, Mayer pointed out, is what Do Not Track means to the companies and websites that will acknowledge the user's call not to be followed. "The [Do Not Track] header has two parts. One is the technology, but the other is what it means to those that support it, what companies will have to do on their end," said Mayer.
"On the technology side, this is an unambiguous win, but on the policy side there is still a lot of work to be done," he said.
According to Mayer, DAA members have not actually agreed to not track users, but to not serve them targeted ads using the data accumulated by tracking cookies, the Web mechanism that can follow users' movements from one site to another.