Data harvesting and sharing by mobile apps is "out of control", University of Oxford researchers have warned. And according to the Financial Times, nearly 90% of free apps on the Google Play store share data with Google's parent company Alphabet
Many free apps track behaviour across many different digital services, which allows companies to build up a detailed profile of people using the app. This data can include age, gender, location, and information about other apps on a smartphone.
The data can then be used for a number of purposes including targeted advertising, credit scoring, or targeted political campaign messages, the researchers point out.
Revenues from online advertising are more than $59bn (£45bn) per year in the US alone, they said. And many people are not aware how data flows from smartphones to advertising groups, data brokers and other intermediaries, Prof Nigel Shadbolt, who lead the research team, told the BBC.
"People [in businesses] are desperate to get as many eyeballs and click-throughs as they can," he said.
Associate professor Max Van Kleek added: "I don't think there's any notion of control."
Data tended to get concentrated by big companies and their subsidiaries. The researchers found that more than 88% of free apps on Google Play shared information with firms owned by Alphabet. Nearly 43% of apps shared data with Facebook, while significant percentages shared data with Twitter, Verizon, Microsoft and Amazon. They also found that news apps - and apps aimed at children - shared information with the largest number of trackers.
In response, Google said: "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."
Google went on to say that it disagreed with the methodology of the study. "It mischaracterises ordinary functional services like crash reporting and analytics, and how apps share data to deliver those services.”
But campaigner Frederike Kaltheuner from Privacy International said that it has become "impossible" for the average user to understand how their data is being used, and to opt out.
"Companies track people... and they use this data to profile and then target people in ways that most of us would find intrusive and very surprising," she said.
"This is no longer about the need to collect data to show 'relevant ads' - this is about profit maximisation at the expense of people's fundamental rights," Ms Kaltheuner added.