July 14, 2011, 4:12 PM — Some online advertising networks continue to track Web users after tracking opt-out requests, even though the networks have promised to honor those questions, according to a new study from Stanford University's Center for Internet Society.
Eight members of the Network Advertising Initiative, a cooperative of online marketing and analytics companies, promise to stop tracking people who use the NAI's service to opt out of targeted advertising, but continue to leave tracking cookies on those people's computers, according to the study, published this week.
The study prompted one U.S. lawmaker to call for Congress to pass new privacy legislation and one privacy group to call for an investigation by the U.S. Federal Trade Commission.
The NAI's opt-out mechanism doesn't require members to stop tracking people, just to stop delivering targeted advertising, noted Jonathan Mayer, lead developer of the Stanford center's new Web measurement tool used to test the opt-out mechanism. Thirty-three of the 64 NAI members that Stanford studied left tracking cookies in place after a Web user opted out of targeted ads, the study said.
The Stanford study blurs the distinction between targeted advertising and online tracking, said Charles Curran, NAI's executive director. While there's a policy debate in Washington, D.C., about do-not-track mechanisms, there's no consensus on what do-not-track means, he said in a blog post.
"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."
Online ad networks may need to continue to gather data for other reasons, such as measuring ad clicks, he wrote.
The Stanford researchers tried to avoid making value judgments, said Mayer, a graduate student at Stanford.
"We recognized our findings, especially with respect to privacy policies, might be controversial," he said. "To the extent possible we tried to present our results objectively and emphasize areas of uncertainty. We tried to not make judgment calls about what companies promised in their privacy policies, and instead relied on the determinations in an earlier Carnegie Mellon study."
Still, privacy advocate Consumer Watchdog called for the FTC to investigate the NAI members that promised to stop tracking, but didn't.