The study by researchers from Georgia Institute of Technology in US examined more than 200 participants who used a custom-built app for Android-based smartphones.

Researchers reviewed the accuracy of personalised ads that were served to test subjects based upon their personal interests and demographic profiles; and examined how much a mobile app creator could uncover about users because of the personalised ads served to them.

Some personal information is deemed so sensitive that Google explicitly states those factors are not used for personalisation, yet the study found that app developers still can discover this information due to leakage between ad networks and app developers.

Mobile app developers choose to accept in-app ads inside their app. Ad networks pay a fee to app developers in order to show ads and monitor user activity – collecting app lists, device models, geo-locations, etc, researchers said.

This aggregate information is made available to help advertisers choose where to place ads. Advertisers instruct an ad network to show their ads based on topic targeting (such as "Autos & Vehicles"), interest targeting (such as user usage patterns and previous click throughs), and demographic targeting (such as estimated age range), they said.