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Our work focuses on a different actor in the broader tracking ecosystem: individuals who can – with a modest budget – purchase ads from advertising networks. We ask: what types of information can these individuals learn about users, and at what cost?

A variety of advertising services are accessible to individuals with a modest budget ($1,000 or less) and a website. Advertising can be used by the individuals buying ads to track a target’s location in relative real-time. Advertising can be used by individuals buying ads to determine which apps a target uses and when, for apps with ads.

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