Nanotargeting Risks: The Urgent Need for Better Privacy Protections

30 May 2024


(1) Ángel Merino, Department of Telematic Engineering Universidad Carlos III de Madrid {};

(2) José González-Cabañas, UC3M-Santander Big Data Institute {}

(3) Ángel Cuevas, Department of Telematic Engineering Universidad Carlos III de Madrid & UC3M-Santander Big Data Institute {};

(4) Rubén Cuevas, Department of Telematic Engineering Universidad Carlos III de Madrid & UC3M-Santander Big Data Institute {}.

Abstract and Introduction

LinkedIn Advertising Platform Background



User’s Uniqueness on LinkedIn

Nanotargeting proof of concept


Related work

Ethics and legal considerations

Conclusions, Acknowledgments, and References


10 Conclusions

This work contributes to the body of literature demonstrating that a few non-PII data items are enough to uniquely identify a user among a user base of tens or hundreds of millions of users. Our work shows that online privacy is very vulnerable, and anonymizing unique identifiers is not enough to hide users’ identities and protect them from being targeted.

The main contribution of our work is that we have shown for the first time that publicly available data can be exploited by third parties to potentially target hundreds of millions of users with hyper-personalized messages individually. Such an attack just requires retrieving information publicly available in the profile of the targeted individual and using it to define the target audience of an ad campaign.

Nanotargeting may expose users to privacy risks derived from malicious activities such as malvertising, manipulation, or blackmail. In our opinion, our work unveils a huge privacy gap that has to be urgently covered. Unfortunately, LinkedIn considers the outcome of our research cannot be considered a vulnerability based on the answer we received to the responsible disclosure process we initiated following the channel suggested by LinkedIn. We propose two immediate actions to mitigate the undesirable effects unveiled by our research.

First, social media platforms must immediately react to impose effective countermeasures that preclude advertisers from running nanotargeting campaigns based on combinations of non-PII attributes. The solution is extremely simple. LinkedIn and other social media platforms exploiting online advertising have to effectively impose their policy where they inform advertisers that they do not allow running campaigns targeting less than 300 users. We struggle to understand why LinkedIn is failing to implement that policy since, in our opinion, they do not have any clear incentive for not doing it. Unfortunately, the reaction of LinkedIn to our responsible disclosure procedure is quite disappointing since they do not consider the bug unveiled in our work as a vulnerability.

Second, our work discusses the practical limitations of the current definition of personal data in the GDPR to assess whether a combination of non-PII elements should be considered personal data. This generates uncertainties in the efficient application of the GDPR since demonstrating whether a combination of certain non-PII items allows uniquely identifying a user may be a very complex task, even for companies and regulators. Data protection authorities should work with the research community to elaborate a guide of good practices in managing non-PII data. This guide should define a clear ground for companies regarding when they should consider combinations of non-PII as personal data. At the same time, that guide may also help citizens to better identify potentially risky situations for their privacy.


This work has been partially funded by the following projects: the project TESTABLE (Grant 101019206) funded by European Union’s Horizon 2020 programme; the project AUDINT (Grant TED2021-132076B-I00) funded by the MCIN/AEI/ 10.13039/501100011033 and the EU FEDER funds; the project UE-MEASURE-CM-UC3M funded by the Madrid Government (Comunidad de Madrid-Spain) under the Multi-annual Agreement with UC3M (“Fostering Young Doctors Research”); the A2 PRIVCOMP funded by the Ministerio de Asuntos Económicos y Transformación Digital and the European Union-NextGenerationEU.


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This paper is available on arxiv under CC BY-NC-ND 4.0 DEED license.