A Wall Street Journal investigation has revealed that a worryingly high number of smartphone apps are sharing data without a user's permission.
The newspaper's examination of 101 smartphone applications for both Apple's iOS and Google's Android operating systems found that 56 sent the handset's unique ID code to other companies without the user's knowledge.
Just under half transmitted phone location data and five shared personal details, including age and gender, to third parties.
iPhone messaging app TextPlus 4 was found to be amongst the worst offenders, sharing the phone’s unique ID to eight ad companies. The application also sent the phone’s post code, and the users’ age and gender to two of them.
In response, Apple said that iPhone apps cannot share data without users' permission and providing them with information as to how the data will be used.
Google also claims that Android apps are required to tell users exactly what data sources it will access, allowing users to choose whether to download it or not. But the WSJ insists that these rules are violated by numerous applications.