Your iPhone is tracking your movements every day, whether you like it or not.
Former Apple employee Pete Warden and data visualisation scientist Alasdair Allan have unearthed data hidden inside iOS back-up files that enables your wanderings to be tracked using GSM cell tower data, so you don't even have to have core location turned on.
The pair have developed an open source tool which extracts the data and overlays it on a world map, and the results are truly scary.
I tested it out on my own iPhone and the results show every place I have visited since I bought my iPhone 4 on launch day last summer.
The creators of the app have hobbled the accuracy of the location finding, displaying the movements in a grid pattern rather than showing actual locations at the highest levels of zoom, in order to prevent the software from being used for nefarious purposes, but the underlying data pinpoints locations within a few metres.
The data is stored in an SQLight file called consolidated.db which is full of latitudes, longitudes, time stamps and cell IDs.
In simple terms, anyone who has access to your iTunes backups of your iOS device from the day iOS4 was installed can find out exactly where you have been and when.
Perhaps the scariest point is that, as the data is stored on your host computer, it persists even when you upgrade devices.
More info in the video below.