The privacy implications of Wi-Fi access point scanning is often overlooked but presents a risk if the information is abused, according to the study, written by the Technical University of Denmark, the Massachusetts Institute of Technology and the University of Copenhagen.
Wi-Fi information isn't considered location data, and Android applications such as Candy Crush Saga, Pandora and Angry Birds routinely collect it.
"This makes it possible for third party developers to collect high-resolution mobility data under the radar, circumventing the policy and the privacy model of the Android ecosystem," wrote Sune Lehmann, an associate professor at DTU Informatics at the Technical University of Denmark, in a blog post.
The study said it wasn't suggesting that Candy Crush Saga, Pandora and Angry Birds collected Wi-Fi scans for location purposes but that they would, in theory, have the ability to do so.
Location data is seen as valuable for purposes such as advertising, where context-specific ads can be shown as a person moves into a certain area. But that sort of tracking has raised privacy concerns over how users are notified that the tracking is taking place and if they can opt out.
The researchers tracked 63 students over six months. Since people tend to have regular movement patterns, "a few most prevalent routers can work effectively as proxies for their location," the study said.
A third party that can get access to Wi-Fi access point scans from a device without authorized access to location data can still "effectively determine the location of each individual 90 percent of the time." For some students, just four access points could describe their approximate location most of the time, it said.
Android applications usually have a set of permissions that someone who installs an app must approve. But the permission for Wi-Fi scanning is separate from the one asking for location data, and granting the permission generally isn't considered risky, the study said.
The study notes that Apple introduced in iOS 8 a method to make it more difficult for Wi-Fi access points to collect consistent data on devices. iOS 8 will spoof a device's MAC (media access control) address.
But Lehmann wrote that Apple's method doesn't address the problem in the study "where data is collected by an application on the phone, not by external devices."
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