Privacy International analysed 34 apps on the Android mobile operating system with user bases of between 10 and 500 million.
The charity began the study after the scandal surrounding the now defunct London based political consultancy Cambridge Analytica, which was accused of improperly obtaining personal information on behalf of political clients and using it to influence the outcome of the US 2016 presidential election or the UK Brexit referendum.
Privacy International researchers found that 23 apps sent data to Facebook the moment a user opened them.
Their report, which was presented at Chaos Computer Congress in Leipzig, Germany, stated: "Facebook routinely tracks users, non-users and logged-out users outside its platform through Facebook Business Tools. App developers share data with Facebook through the Facebook Software Development Kit (SDK), a set of software development tools that help developers build apps for a specific operating system."
