No surprises: measuring intrusiveness of smartphone applications by detecting objective context deviations

We address the challenge of improving transparency for smartphone applications by creating tools that assesses privacy risk. Specifically, we invented a framework for qualitatively assessing and quantitatively measuring the intrusiveness of smartphone applications based on their data access behaviors. Our framework has two essential components. The first component is the Privacy Fingerprint, a novel visualization that is concise yet holistic. It captures each app's unique access patterns to sensitive personal data, including which types of behaviors and under which privacy-relevant usage contexts the data are collected. The second component is a new Intrusiveness Score that numerically measures out-of-context data collection, based on real data accesses gathered from empirical testing on 33 popular Android apps across 4 app categories. Specific attention is paid to the proportion of data accesses that occurs while the user is idle, raising the perceived level of intrusiveness and exposing the profiling potential of an app. Together, these components will help smartphone users decide whether to install an app because they will be able to easily and accurately assess the relative intrusiveness of apps. Our study also demonstrates that the Intrusiveness Score is helpful to compare apps that exhibit similar types of data accesses.