As of today, three browser manufacturers have answered that call. Google's Chrome, Mozilla's Firefox and Microsoft's Internet Explorer 9 have all released their own versions of do-not-track. None of the three, however, are foolproof.
Microsoft's IE9, which rolled out today, allows users to input blacklists of ad networks and other companies. Users' calls to those companies' servers won't be put through when they appear as third parties. That approach can effectively block all ads served by behavioral targeting companies.
While this approach can effectively block ad networks -- and other third parties who land on blacklists -- it doesn't guarantee that users won't be tracked. For one thing, the burden is on users to create blacklists, or download those provided by privacy groups. TRUSTe, for one, intends to create a blacklist that will include ad networks that don't participate in self-regulatory programs. Other groups intend to create blacklists that encompass all ad networks. Some Web users who care about privacy undoubtedly will be technically savvy enough to select a blacklist and input it, but many likely will decide the project is too complicated.
Secondly, there's no guarantee that the blacklists put out by various organizations will be accurate -- especially given the speed at which Web companies come and go. Currently, industry watchers aren't even certain how many companies are collecting data about Web users for behavioral advertising purposes. Currently around 300 companies are thought to collect data used for behavioral targeting, but CEO TRUSTe Chris Babel tells MediaPost that number could quickly balloon if some of the companies that currently collect analytics data expand into behavioral advertising.
Mozilla's Firefox do-not-track header also offers no guarantees, though for different reasons. When a user activates the header, it alerts every site visited that the user doesn't wish to be tracked. But ad networks need not honor the header.
Google's Chrome now offers a track-me-not extension that allows users to permanently opt out of tracking by companies that participate in the industry's self-regulatory program. As of now, however, not all ad networks do so. And even when networks do offer opt-outs, the links don't always work.
Meanwhile, lawmakers seem to be growing impatient with Web companies' voluntary efforts to ensure that consumers can decide whether or not to be tracked. Reps. Bobby Rush (D-Ill.) and Cliff Stearns (R-Fla.) have each said they will soon introduce privacy bills, while Rep. Jackie Speier (D-Calif.) intends tomorrow to introduce the Do Not Track Me Online Act. That measure would authorize the Federal Trade Commission to create regulations ensuring that consumers can opt out of online tracking.