Do Not Track is back in the spotlight today as senators Jay Rockefeller (D-W.Va.) and Richard Blumenthal (D-Conn.) reintroduced a bill that would let people opt out of having their online activity tracked by advertisers. Originally introduced in 2011, the Do Not Track Online Act was envisioned as an online equivalent to the nationwide Do Not Call list, but talks have broken down between privacy activists and the ad industry, and nearly two years since its initial proposal, there is still no consensus about how to move forward.

The technical implementation of Do Not Track uses an HTTP header — a single line of code sent with every request for a web page — that tells the recipient you don't want to be tracked online. The goal is to stop the accumulation of browsing data by third parties like advertisers, which use it to sell online ads targeted at individual users. Advertisers have been reluctant to cede any major ground in the negotiations, claiming that "anonymized" tracking is necessary to deliver targeted, relevant ads. Rather than stop collecting browsing information, they have been pushing for implementations that would let users simply opt out of receiving the targeted ads.

The W3C’s Tracking Protection Working Group was formed in 2011 to design the specification needed to actually implement Senator Rockefeller’s legislation, but with no signs of a consensus forming, it’s doubtful that re-introducing the bill is going to be enough to break through the impasse. As reported by The Hill, Blumenthal criticized advertisers for their lack of progress on the issue, saying "industry stood at the White House and made a public pledge to honor do-not-track requests, but has since failed to live up to that commitment."