What types of user data are mobile apps sending to third parties? We chose 110 of the most popular free mobile apps as of June-July 2014 from the Google Play Store and Apple App Store, across 9 categories likely to handle potentially sensitive data about users including job information, medical data, and location. For each app, we used a man-in-the-middle proxy to record HTTP and HTTPS traffic that occurred while using the app and looked for transmissions that include personally identifiable information (PII), behavior data such as search terms, and location data, including geo-coordinates. An app that collects these data types may not need to notify the user in current permissions systems. Results summary: We found that the average Android app sends potentially sensitive data to 3.1 third-party domains, and the average iOS app connects to 2.6 third-party domains. Android apps are more likely than iOS apps to share with a third party personally identifying information such as name (73% of Android apps vs. 16% of iOS apps) and email address (73% vs. 16%). For location data, including geo-coordinates, more iOS apps (47%) than Android apps (33%) share that data with a third party. In terms of potentially sensitive behavioral data, we found that 3 out of the 30 Medical and Health & Fitness category apps in the sample share medically-related search terms and user inputs with a third party. Finally, the third-party domains that receive sensitive data from the most apps are Google.com (36% of apps), Googleapis.com (18%), Apple.com (17%), and Facebook.com (14%). 93% of Android apps tested connected to a mysterious domain, safemovedm.com, likely due to a background process of the Android phone. Our results show that many mobile apps share potentially sensitive user data with third parties, and that they do not need visible permission requests to access the data. Future mobile operating systems and app stores should consider designs that more prominently describe to users potentially sensitive user data sharing by apps.
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