Almost nine out of ten free apps available via the Google Play store are sending back information on their user's to Google's parent company, new research has found.
According to a study conducted by the University of Oxford, the level of data sharing from these apps is "out of control", with nearly 90 per cent of mobile tools sharing user details with Alphabet.
Meanwhile, more than four out of ten apps (43 per cent) sent data to Facebook, while Twitter, Microsoft and Amazon also received user details from a significant percentage of free apps.
News apps were among those that shared information with the largest number of trackers, along with apps aimed at children.
Typical data shared includes age, gender, location and information about what other apps are installed on a smartphone. This is enough to build a detailed profile of a user, which can then can be used for a range of purposes, from advertising and credit scoring to sending targeted political messages, the researchers stated.
Professor Nigel Shadbolt, who led the study, told the BBC that many people are unaware how data flows from smartphones to advertising groups, data brokers and other intermediaries, adding: "People [in businesses] are desperate to get as many eyeballs and click-throughs as they can."
His colleague and fellow researcher Max Van Kleek added: "I don't think there's any notion of control."
Responding to the study, Google said it disagreed with the researchers' methodology, arguing that it had mischaracterised functional services, such as analytics and crash reporting, and how apps share data for these features.
It added: "Across Google and in Google Play we have clear policies and guidelines for how developers and third-party apps can handle data and we require developers to be transparent and ask for user permission. If an app violates our policies, we take action."