Smartphone security firm Lookout Labs has released a free tool for Android that it says can show what data ad networks are accessing on a user's phone .
The Ad Network Detector is a relaunched version of the company's Push Ad Detector, released to beta several weeks ago.
It scans apps for the presence of 35 ad networks and warns users what personal information the networks are collecting.
The tool was originally created to warn users of "ad networks that are capable of pushing out-of-app ads to the default Android notification bar, placing generically designed icons on the mobile desktop, and changing browser settings, like bookmarks or homepage".
Advertisement-supported apps are a popular way for developers to make money while keeping the cost of the app free.
Google already warns users of the types of personal information that an app has access to, prior to a user downloading it.
However, it does not warn users what ad networks that are embedded within apps are accessing and collecting.
The app's release comes the same week ad networks pledged to provide an opt-out method for tracking users, while US President Barack Obama proposed a bill of rights protecting citizens' privacy online.