The data, consisting of latitude and longitude coordinates and corresponding timestamps, is stored unencrypted and, apparently, without conspicuous notification. Apple did not respond to a request to explain whether any of its user agreements cover this practice.
The existence of the iPhone tracking database was disclosed on Wednesday at the Where 2.0 conference by Alasdair Allan, an iPhone programmer and a senior research fellow in Astronomy at the University of Exeter, and Pete Warden, founder of OpenHeatMap.com and a former Apple software engineer.
French blogger Paul Coubis appears to have been the first to report this issue last year, though his findings didn't attract much attention.
Apple's storage of iPhone user location data began with the arrival of iOS 4. Allan and Warden speculate that Apple began storing the data because it would be useful for the background location and geofencing capabilities in iOS 4.
Apple's actions may result in litigation because its data collection is similar in some respects to what Google was doing when it unwittingly allowed its Street View cars to collect information from open Wi-Fi networks without disclosure. While Apple's software is not collecting actual packet data traveling over Wi-Fi as Google did, it is recording the MAC addresses of Wi-Fi access points near the iPhone owner being tracked.
Allan and Warden have written and posted an open source Mac OS X application to provide Mac-using iPhone users with a way to examine their stored location data trail.
While both men believe Apple should have disclosed what it was doing more clearly, they say there's no reason to be alarmed because the data remains in the user's possession and isn't disclosed. But they do recommend that users encrypt the data through the "Encrypt iPhone Backup" setting under the "Options" menu in iTunes.
Mobile service providers already have this information. German Green party politician Malte Spitz recently made waves in Germany when he obtained and published data from Deutsche Telekom that detailed his movements.
While location data isn't generally available without a court order--unless deliberately disclosed through some social location service--there are still legal battles being fought to make sure that constitutionally-guaranteed privacy protections safeguard data on mobile phones.
Now that iPhone users are known to carry detailed histories of where they've been on their phones and on their computers, those in an adversarial position--litigious spouses or employers, or law enforcement personnel, for example--may choose to seek location data where it is readily accessible rather than attempting to pry it from a mobile service provider through legal process.
If it's any consolation, Allan and Warden said that a lot of the data is inaccurate.