In response to privacy concerns about pervasive online tracking by advertisers and others, Congress introduced the Do Not Track Online Act of 2011. Inspired by the success of the national Do Not Call registry, privacy activists were hopeful that a similar approach could be taken online, and the internet's largest standards-making body, the W3C, formed a working group to come up with a solution. That solution took the form of an HTTP header — a small piece of code that tells its recipient that this user wants to opt out of tracking.

In the nearly two years since the legislation was introduced, not much has changed. While there might be broad agreement about how Do Not Track should be implemented, there is no consensus on what those who receive the header should (not) be required to do. Do Not Track is now supported in all major browsers, including Internet Explorer 10, which drew fire for its implementation.

The Do Not Track Online Act is now being re-introduced, and senator Jay Blumenthal has been harshly critical of the ad industry's commitment, accusing companies of "dragging their feet." Whatever the fate of Do Not Track, browser makers have shown that they aren't afraid of implementing technical solutions to protect user privacy, with Firefox being the most recent to block third-party cookies by default.