According to the IAB's Zaneis, there is more potential for privacy violations when you're dealing with the big ecosystems.
In contrast, Zaneis argues, the tracking data that most third-party digital advertising companies collect contains no personally identifiable information.
In addition, Facebook's "Like" buttons -- and other social network buttons that appear on many websites -- actively track user activity on those pages and send data back to the social networks. "It's unclear whether the mere presence of a button on a page gives Facebook or Google first-party status," Chapell says. "We've created these artificial distinctions, but there's no real privacy gain. You'd think the bigger companies would be the ones you'd want to target [with Do Not Track]."
Further complicating matters, the opt-in nature of the DNT program has been "hijacked" by some routers and security packages that automatically turn on the DNT header by default, such as the anti-malware software from AVG, says Zaneis. "Anything that sits between the browser and the website can inject the DNT signal. It no longer represents a consumer choice," he adds.
Zaneis sees Microsoft's decision to turn on DNT by default when users install Internet Explorer in a similar fashion. For this reason, he says, at least one major Web publisher that honors DNT signals from other browsers has declined to do so for IE users.
In the meantime, Mozilla and other browser vendors let users decide whether or not to turn on the DNT signal. "We have no plan to turn on DNT by default in Firefox. It is a representation of the user's preference and not Mozilla's," says Alex Fowler, head of privacy and public policy at Mozilla.
The issues regarding who should be allowed to set a DNT signal -- including the level of explanation that must be provided before a user is deemed to have intended to turn it on -- have been resolved within the emerging technical standard that's about to be put forward, Brookman says.
So what happens next?
Efforts in the W3C working group are continuing, but Zaneis thinks the most likely scenario is that the industry will work with "a few key players" to develop a policy that's an extension of a self-regulatory program developed by the Digital Advertising Alliance (DAA), an industry consortium.
Last fall, when frustrations over the W3C Tracking Protection Working Group's lack of progress came to a head, the DAA quit the group and formed its own DNT subcommittee. "We are working with key interest groups to develop principles to incorporate browser signals into the existing DAA program. Think of it as the compliance piece that will be lacking from the W3C process," Zaneis says.
Sign up for CIO Asia eNewsletters.