Some Web Advertisers Continue to Track Users Who Opt Out

12 October 2012

A recent study at the Stanford University’s Center for Internet and Society shows that some ad networks are continuing to track Web users, even when those users have requested to opt out of such tracking.

According to the study, eight members of the Network Advertising Initiative, a cooperative of online marketing and analytics companies, have pledged to stop tracking people who use the NAI’s service to opt out of targeted advertising, but actually use tracking cookies, HTML5 storage, and fingerprinting on those computers.

The study found that half of the NAI members tested did not remove their tracking cookies after users opted out, says Jonathan R Mayer, a Stanford graduate student studying computer science and law.

“Of the 64 companies we studied, 32 left tracking cookies in place after opting out,” says Mayer.

Mayer says that at least eight NAI members promise to stop tracking after opting out, but nonetheless leave tracking cookies in place.

“We compared our results to a survey of NAI member privacy and optout policies recently conducted by Carnegie Mellon's CyLab. We identified seven companies that promise to stop tracking when a user opts out, but nonetheless leave their tracking cookies in place,” he says.

The study also found that at some NAI members go beyond their privacy policies and remove their tracking cookies, Mayer said. “In comparing our results to the Carnegie Mellon study of privacy policies, we found that ten NAI members remove their tracking cookies upon opting out, even though they promise to only stop behavioral targeting of ads.”

Charles Curran, NAI's executive director, said the study may confuse users by blurring the distinction between “Do Not Target” choices offered by online advertisers, and new browser technologies that offer users the promise of not being “tracked.”

Under the NAI self-regulatory code, companies commit to providing an opt out to the use of online data for online behavioral advertising purposes, Curran said. “But the NAI code also recognizes that companies sometimes need to continue to collect data for operational reasons that are separate from ad targeting based on a user's online behavior.”

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