The nation’s top wireless carriers say they all collect personal information, including location data, about subscribers and use much of that information to tailor marketing pitches for more services.

In letters responding to lawmakers’ questions, they described varied policies on protecting data and how long they retain location and other sensitive information such as a user’s name, Social Security number, and address.

The queries to the carriers by Reps. Edward Markey (D-Mass). and Joe Barton (R-Tex.) come amid increased scrutiny of privacy on mobile devices and questions about how Apple and Google store data on users’ locations.

Researchers earlier this week published a report revealing that a file on the Apple iPhone stored time-stamped location data. Google acknowledged last week that it collects anonymous tracking data for its location services, including from phones that run Android software, but said that the information is recorded only when users give permission.

“The use of encryption and related security technologies were utilized to varying degrees across the four wireless carriers, and sensitive data was retained for differing periods of time,” Markey said. “Personal data should be made unreadable to those without a legitimate need to access it to the greatest extent possible, and the data should not be retained longer than absolutely necessary. Otherwise, there is a heightened risk of security breaches that expose consumers to identity theft and other crimes.”

AT&T said it is in the process of encrypting all sensitive personal information about its users such as credit card numbers, date of birth and specific data on a person’s location. It said it disposes of location-based information within five years.

T-Mobile was more vague about its data retention and security program. The company said only that it keep personal information “as long as we have a business need, or as applicable laws, regulations, or government order require.” It did not say whether personal information is encrypted. A spokesman did not immediately respond to a request for comment.

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