A new data set obtained from a US data broker reveals for the first time about 40,000 apps from which users‘ data is being traded. The data set was obtained by a journalist from netzpolitik.org as a free preview sample for a paid subscription. It is dated to a single day in the summer of 2024.

Among other things, the data set contains 47 million “Mobile Advertising IDs”, to which 380 million location data from 137 countries are assigned. In addition, the data set contains information on devices, operating systems and telecommunication providers.

Ths investigation is part of an international cooperation by the following media: Bayerischer Rundfunk/ARD (Germany), BNR Nieuwsradio (Netherlands), Dagens Nyheter (Sweden), Le Monde (France), netzpolitik.org (Germany), NRK (Norway), SRF/RTS (Switzerland) and WIRED (USA).

Overview of our findings

• The approximately 40,000 apps in the new dataset cover a wide range of categories, from gaming, dating and shopping to news and education. They include some of the most popular apps worldwide, with millions of downloads in some cases.

• For a smaller number of apps, the data set contains alarmingly precise location data. This data can help to identify a person’s place of residence. These apps include the queer dating app Hornet with more than 35 million users; the messaging app Kik with more than 100 million downloads in the Google Play Store alone; Germany’s most popular weather app Wetter Online, which also has more than 100 million downloads in the Google Play Store; and the flight tracking app Flightradar24 with more than 50 million downloads in the Googles Play Store; the app of German news site Focus Online and classifieds apps for German users (Kleinanzeigen) and French users (leboncoin).

• For a bigger number of apps, less precise locations which appear to have been derived from IP addresses can be found in the data set. This list includes popular apps such as Candy Crush, Grindr, Vinted, Happy Color, dating apps Lovoo and Jaumo, news aggregator Upday, German email apps gmx.de and web.de as well as the popular dutch weather app Buienalarm.

• Since the sample only covers one day, it is difficult to identify people based on their locations from this data set alone. However, in combination with other data sets from the advertising industry, which the research team obtained from data brokers, it’s possible to identify and track people on a large scale. The location data might for example provide clues to their home and work addresses.

• Thus, the team was able to identify users of Wetter Online in Germany and Kik in Norway. The individuals confirmed that the data must belong to their devices and their use of the respective apps.

• Location data aside, the mere information about who uses which apps can already be dangerous. For example the data set includes numerous Muslim and Christian prayer apps, health apps (blood pressure, menstruation trackers) and queer dating apps, which hint at special categories of personal data under GDPR.

Where did the data set come from?

The research team obtained the data set from US data broker Datastream Group, which now uses the name Datasys. The company did not respond to multiple requests for comment.

Contact with the data broker was established through Berlin-based data marketplace Datarade. The company states in response to inquiries that it does not host any data itself. According to a spokesperson „Data providers use Datarade to publish profiles and listings, enabling users to contact them directly“. Datarade „requires data providers to obtain valid consent in case they’re processing personal data and to aggregate or anonymize data in case they’re processing sensitive personal data“.

Where does the data originate?

According to our analysis, the data originates from Real Time Bidding (RTB), which is a process in the online advertising ecosystem. These are auctions in which advertising inventory of apps and websites is sold. In the process, apps and websites send data about their users to hundreds or thousands of companies. These data contains the information that we can see in our dataset. There have already been multiple warnings that advertising companies are collecting the data from RTB in order to sell it – often without the knowledge or explicit consent of the users or their apps.

What the apps say

None of the apps we confronted so far states they had business relations with Datastream Group / Datasys. The apps Hornet and Vinted for example wrote, that they cannot explain how their users‘ data ended up with data brokers. Queer dating app Hornet emphasizes that it does not share actual location data with third parties and announces an investigation. Other companies such as Kik, Wetter Online, Kleinanzeigen, Flightradar, Grindr and King, the company behind the game Candy Crush, did not respond to press inquiries.