To show users the data recorded by Apple's devices, Allen and Warden created a Web application that plots a user's iPhone data on a map. Once downloaded to the computer users sync with their Apple device, the application scans through backup files to look for the hidden file with the location information. When it finds the relevant file, the application shows the location history on a map.
The researchers said they believe that the coordinates of the phone are determined by cell-tower triangulation. The location data aren't always precise, but they said the phones may have recorded up to tens of thousands of data points. However, there's no evidence that the data is being transferred beyond the devices or computers that sync with them, they said.
Digital rights activists say that this latest Apple finding is another example of the risks related to location information.
"These location records can reveal a wealth of sensitive information about you: your attendance at a gun rally or prayer meeting, your frequent visits to a health clinic and more," said Chris Conley, a technology and civil liberties fellow at the ACLU of Northern California. "Control over this information needs to be in your hands, not Apple's."