Your favorite mobile apps leave a trail of cookie crumbs

Instagram's cookies and unencrypted Web traffic give you up to anyone watching packets pass by.
Sean Gallagher

Most people know the privacy risk of Web cookies—the bits of data that Web browsers store and return to websites to help them keep track of your credentials, where you are in an application, and other information. Advertisers, social media services, and search engine providers use cookies to track users' travels on the Web to target them for advertising. And as we’ve reported, those cookies can be used by someone surveilling Web traffic to track you as well.

But when people use mobile applications, they’re also vulnerable to the same sort of cookie tracking. Many mobile apps are just Web applications wrapped in a package for an app store—they send cookies back to the same server to identify the user and provide location information and other data about a device to the application vendor, third parties, or anyone who happens to be watching network traffic. Taken together with other data, these cookies can be used to track individuals as they wander the world, posing a significant privacy risk.

There are other components of the Web content consumed by mobile apps that can be used in tracking. Some use REST interfaces that pass data as part of their requests back to servers, and that data is often sent in the clear. JavaScript elements within Web content can also access local device data and send it back as a data structure; this data is often sent unencrypted as well, and the process follows a common enough format for hackers or intelligence organizations to reverse engineer it.

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