A group of computer engineers wrote a computer program called TaintDroid and installed it on a smartphone to monitor how 30 apps - mobile phone programs for the likes of social networking and downloadable games - were using sensitive information.
Of the 30 applications, 15 sent sensitive information, including the phone's location, to several advertising companies' servers.
TraintDroid's findings suggest that smartphones are becoming another outlet for advertisers to track people. The applications assessed included BBC News Live Stream, MySpace and Solitaire, which can be downloaded on smartphones using the popular Google-owned Android operating system.
Using a technique called ''taint tracking'', the researchers tagged sensitive information held within their test phone, such as the phone's ID numbers and location, which can be traced when accessed by an application or if it leaves the phone via its wireless internet connection.
The study's lead author, William Enck, who is completing his PhD at Pennsylvania State University, said: ''We were surprised by how many of the studied applications shared our information without our knowledge or consent.''
A spokeswoman from Google said on all computing devices, desktop or mobile, users needed to entrust at least some of their information to the developer of the application.
''We provide developers with best practices about how to handle user data.''
Users were also free to uninstall applications at any time, the spokeswoman said.