Google proposes another interest-based ad system • The Register

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Google has abandoned Federated Learning of Cohorts (FLoC), a categorization system for serving interest-based advertising, and has replaced it with Topics, a categorization system for serving interest-based advertising.

Caught between the push to do something about cookie-based tracking and the counter-revolution to get regulators to keep third-party cookies alive, the chocolate factory has proposed an overhaul of its ill-fated FLoC plan.

“With Topics, your browser determines a handful of topics like ‘Fitness’ or ‘Travel & Transportation’ that represent your top interests for that week based on your browsing history,” explained Vinay Goel, product director for Google’s Privacy Sandbox, in a blog post on Tuesday.

In other words, your web history is broken down into hostnames, which are analyzed by a machine learning algorithm to determine the general topics of interest to you. This all happens locally in your browser. Then, websites aware of this technology can send a Google Topics API call to your browser to retrieve a set of up to three topics derived from your visited websites, which can then be used to serve targeted ads present.

In an alleged nod to privacy, themes are selected on the user’s device without involving external servers – although ad networks and the like may be able to shut down which themes prompted their ads – and stored for just three weeks before being deleted will. And the themes have been “carefully curated to exclude sensitive categories like gender or race,” we’re told.

“When you visit a participating site, Topics selects just three topics, one from each of the past three weeks, to share with the site and its advertising partners,” Goel said. “Themes allow browsers to give you meaningful transparency and control over this data, and in Chrome we’re creating user controls that allow you to see the themes, remove any you don’t like, or disable the feature entirely.

“Themes are selected entirely on your device with no involvement of external servers, including Google servers.”

But even this latest move could fall short, at least as far as privacy advocates are concerned. Researchers have already established that a person’s browsing history can be used to uniquely identify someone.

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Launched in 2020, FLoC was tested for a few months last year until privacy issues surfaced. FLoC was one of several proposals to keep targeted advertising after third-party cookies are phased out, as they are irrevocable monitoring features.

Google collectively refers to these proposals as the Privacy Sandbox. Not only do they reflect the realization that web browsers have real security and privacy vulnerabilities, but also that tightening privacy laws in Europe and the US will not allow online advertising to continue in its current invasive form.

FLoC divides people into groups with similar interests in order to hide individual identities in the crowd and still pitch people with marketing that matches supposed interests. Google previously claimed that FloC is 95 percent as good as cookie-based advertising.

However, a technical analysis of the proposal [PDF] published last June by Mozilla’s Eric Rescorla and Martin Thomson suggests that Google’s technology does not offer sufficient anonymity.

“In particular, it may be possible to identify individual users using both FLoC IDs and relatively weak fingerprint vectors,” the Mozilla researchers concluded. “If FLoC is viewed as coexisting with existing state-based tracking mechanisms, it has the potential to significantly increase the power of cross-site tracking.”

At the same time, Google has come under attack from advertising industry challengers who argue that browser cookies should be left alone as their businesses rely on cookie-based data collection. Revenge-driven advertising firms have tried to convince antitrust authorities that removing third-party cookies will only make Google more powerful because Google retains data-gathering opportunities while others don’t.

The changes are anti-competitive because they raise barriers to entry and eliminate competition in the exchange and ad buying tool markets

This reasoning is reflected in the antitrust complaints Google is facing in the US, such as that filed by Texas and other states, which describe the privacy sandbox proposals as follows: “Overall, the changes are anticompetitive because they raise and eliminate barriers to entry Competition in the ad exchange and ad buyer markets, further expanding the already dominant market power of Google’s advertising business.”

In a blog post responding to Google’s announcement, Peter Snyder, senior director of privacy at rival browser maker Brave, characterized Topics as a rebranding of FLoC that fails to address important privacy issues.

Topics, he said, differs from FLoC by conditionally transferring interests rather than making them available on demand and by adding some randomness to make user re-identification via fingerprinting techniques a bit more difficult.

Despite this, he argues that these changes still amount to putting lipstick on a pig. Both FLoC and Topics, he claims, harm privacy and competition. The choice, he argues, should not be the lesser of two evils.

“Google’s proposals only improve privacy from the cynical, self-serving baseline of ‘better than Google today,'” Snyder said. “Chrome is still the most popular privacy-violating browser out there, and Google is trying to solve a problem they’ve introduced by taking small steps to solidify their dominance in the advertising technology landscape. Topics does not solve the core problem of Google broadcasting user data to websites, including potentially sensitive information.” ®

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