Credit cards are true gold mines for digging personal data: consumption habits, living standards, travels… they keep track of some of the juiciest information for investment and research companies, banking institutions or brokers. Motherboard (VICE) recently unveiled the practices of Yodlee, with the publication of a confidential file revealing the fact that the leading US banking data broker does not anonymize its clients’ data. Yves-Alexandre de Montjoye, assistant professor at Imperial College London, explains that even if personal information such as telephone numbers or e-mail addresses are not disclosed, individuals can still be identified if someone “has access to the data set and to certain information about the individual, such as stores he or she visited and when”. The professor demonstrated his argument in 2015 by retrieving the identities of three individuals from a database of over 1.1 million credit card transactions over the last three months. The majority of the banking data collected by Yodlee relates to the customers of its main partners: Bank of America, Citigroup and HSBC. With the advent of neo-banks such as Revolut or N26, which are entirely digitized, there is cause for concern about the amount of customer data collected – indeed, the British bank Revolut, created in 2015, plans to acquire 100 million additional customers by 2025 (Source : Presse-Citron).