Apple and Google are scrambling to regain trust after revelations about the way smart phones and tablets handle users' location data. In a U.S. Senate subcommittee hearing held today, representatives from Apple and Google stressed that their companies had streamlined and clarified their handling of location-based data. But a key unanswered question is how they'll let third-party app providers share that information.

The problem is that users enjoy location-based services, but most don't understand what happens to the data they share in exchange for using those services. Senators wondered if location data was being stored securely enough to protect users. They pointed to the lack of privacy policies for many mobile apps, and noted that even when users are aware of what happens to their data, they may find it difficult to control.

For example, until Apple's update to iOS last week, someone who opted out of location services wasn't actually turning off all of his device's location-based sharing. Apple said the problem was due to a bug that has since been corrected.

Guy "Bud" Tribble, vice president of software technology for Apple, testified that "Apple does not track customers' locations. Apple has never done so and has no plans to do so."

Tribble said that the location information found on phones represented a portion of a crowd-sourced database that Apple maintains in order to process location information more rapidly than is possible through GPS alone. The company stores the locations of cell towers and Wi-Fi hot spots collected from millions of devices. User devices note which towers and hot spots they can connect to, and use that to quickly deduce location. He said that the information stored on iPhones was never a user's location.