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How Alice Can Buy Ads to Track Bob

Research. Can regular people, not just impersonal, commercially-motivated merchants or advertising networks—can exploit the online advertising ecosystem to extract private information about other people? The answer is yes. A new study documents that.

For example, an individual or small group with a $1000 US Dollar budget can use targeted ads to track the locations of targeted individuals as they move from home, to work, and to other sensitive locations. The researcher also found that they can target ads to users of specific applications and at specific locations, which means that one can use purchased ads to count the number of Grindr (a gay online dating app) users or Quran Reciters (a religious app) users in a house. They found that they can use targeted ads to learn when a person is using a specific application (e.g., when a targeted individual is using Talkatone, a messaging app); a natural extension could be to observe whether two targeted individuals are using the same app at the same time, thereby yielding potential side-channel information about communications patterns.

Read the study