Security researchers have discovered that Apple's iPhone keeps track of where you go – and saves every detail of it to a secret file on the device which is then copied to the owner's computer when the two are synchronised.
The file contains the latitude and longitude of the phone's recorded coordinates along with a timestamp, meaning that anyone who stole the phone or the computer could discover details about the owner's movements using a simple program.
For some phones, there could be almost a year's worth of data stored, as the recording of data seems to have started with Apple's iOS 4 update to the phone's operating system, released in June 2010.
Here's the app to plot the data on your phone on a map. Yup, it's there!
AT&T saves all that data too, but at least that (theoretically) requires a subpoena. This just requires momentary access to the phone.