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A recent publication* describing a study of 82,501 pre-installed software programs (apps) on 1,742 Android smartphones found that many apps secretly collected user data that was transmitted to the app developers. This included such things as user contacts, emails, telephone metadata, geolocation information, and other user statistics.
*the article, An Analysis of Pre-Installed Android Software, can be accessed at https://www.ftc.gov/system/files/documents/public_comments/2018/08/ftc-2018-0052-d-0036-154998.pdf