Online tracking. Online advertisers make a lot of money by selling user pofiles. How do they track your behavior? Every ad sends back where you visited and a cookie on your browser stores a unique ID so that these visits can be attributed to the same person .
Do-no-track. A new feature called “do not track” has been pioneered by Firefox  and works as follows: If enabled, every request for a web page is accompanied by information (in the HTTP header) that tells online ad providers not to not track your behavior. Browser support is currently as follows:
- Firefox: Firefox 4
- Safari: coming in Mac OS X Lion
- Microsoft: Internet Explorer 9
- Chrome: Google currently only supports “Keep My Opt-Outs” which persists opting out of personlized ads and “related tracking” (does this mean all tracking?).
A spokesman for Google, which is a major player in online advertising, said the company "will continue to be involved closely" in industry discussions about do-not-track. 
- The main problem with do-not-track is that participation for online advertisers is voluntary. What is the incentive for them to comply? Not all of their activity is evil (e.g., they help with financing free web content ), so we should think about a carrot in addition to the do-not-track stick. One idea would be to implement a platform where they can make the case for users to let themselves be tracked (e.g. by compensating them for doing so).
- Why is it opt-in? Shouldn’t not being tracked be the default? In addition to protecting the less technically savvy among us, this would save web traffic.
- How Online Tracking Companies Know Most of What You Do Online (and What Social Networks Are Doing to Help Them)
- More Choice and Control Over Online Tracking [Firefox]
- Apple Adds Do-Not-Track Tool to New Browser [via Mac Rumors]
- Why you shouldn’t ad-block and ideas for better ads