Facebook doesn’t tell users everything it really knows about them

Limiting commercial data brokers’ distribution of your personal information is no simple matter. For instance, opting out of Oracle’s Datalogix, which provides about 350 types of data to Facebook according to our analysis, requires “sending a written request, along with a copy of government-issued identification” in postal mail to Oracle’s chief privacy officer.

Users can ask data brokers to show them the information stored about them. But that can also be complicated. One Facebook broker, Acxiom, requires people to send the last four digits of their social security number to obtain their data. Facebook changes its providers from time to time so members would have to regularly visit the help center page to protect their privacy.

One of us actually tried to do what Facebook suggests. While writing a book about privacy in 2013, reporter Julia Angwin tried to opt out from as many data brokers as she could. Of the 92 brokers she identified that accepted opt-outs, 65 of them required her to submit a form of identification such as a driver’s license. In the end, she could not remove her data from the majority of providers.

ProPublica’s experiment to gather Facebook’s ad categories from readers was part of our Black Box series, which explores the power of algorithms in our lives. Facebook uses algorithms not only to determine the news and advertisements that it displays to users, but also to categorize its users in tens of thousands of micro-targetable groups.

Our crowd-sourced data showed us that Facebook’s categories range from innocuous groupings of people who like southern food to sensitive categories such as “Ethnic Affinity” which categorizes people based on their affinity for African-Americans, Hispanics and other ethnic groups. Advertisers can target ads toward a group — or exclude ads from being shown to a particular group.

Last month, after ProPublica bought a Facebook ad in its housing categories that excluded African-Americans, Hispanics and Asian-Americans, the company said it would build an automated system to help it spot ads that illegally discriminate.

Facebook has been working with data brokers since 2012 when it signed a deal with Datalogix. This prompted Chester, the privacy advocate at the Center for Digital Democracy, to file a complaint with the Federal Trade Commission alleging that Facebook had violated a consent decree with the agency on privacy issues. The FTC has never publicly responded to that complaint and Facebook subsequently signed deals with five other data brokers.

To find out exactly what type of data Facebook buys from brokers, we downloaded a list of 29 000 categories that the site provides to ad buyers. Nearly 600 of the categories were described as being provided by third-party data brokers. (Most categories were described as being generated by clicking pages or ads on Facebook.)

The categories from commercial data brokers were largely financial, such as “total liquid investible assets $1-$24 999,” “People in households that have an estimated household income of between $100K and $125K,” or even “Individuals that are frequent transactor at lower cost department or dollar stores.”

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