Facebook: User shadow data, including phone numbers may be used by advertisers

The worst suspect is a disconcerting reality, Facebook admitted that advertisers were able to access phone numbers of its users for enhanced security.

Researchers from two American universities discovered that that phone numbers given to Facebook for two-factor authentication were also used for advertising purposes.

“These findings hold despite all the relevant privacy controls on our test accounts being set to their most private settings,” reads the study published by the researchers.

“Most worrisome, we found that phone numbers uploaded as part of syncing contacts — that were never owned by a user and never listed on their account – were in fact used to enable PII-based advertising,”

The study investigates the channels used by advertisers can gather personally identifying information (PII) from Facebook, WhatsApp and Messenger services.

The contact lists uploaded to the Facebook platforms could be used by advertisers that once extracted the personal information can leverage it to target people in their networks.

The experts speculate Facebook is using a hidden layer of details it has about its users, like phone numbers used for 2FA authentication, that they called “shadow contact information.”

The study supported concerns that Facebook uses “shadow” sources of data not given to the social network for the purpose of sharing to make money on advertising.

“We use the information people provide to offer a better, more personalized experience on Facebook, including showing more relevant ads.” a spokeswoman told Gizmodo that first reported the news.

Facebook continues to face a severe crisis due to the way it manages data of its users, the Cambridge Analytica case has shocked the world about the way the social network giant has shared the information of its unaware users with third party companies.

At the time of writing, Facebook’s Guy Rosen, VP of Product Management announced that attackers exploited a vulnerability in the “View As” feature to steal Facebook access tokens of 50 Million Users.

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Pierluigi Paganini

(Security Affairs – Facebook, privacy)

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Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.