Online advertising platforms such as those of Facebook and Google collect detailed data about users, which they leverage to allow advertisers to target ads to users based on various pieces of user information. While most advertising platforms have transparency mechanisms in place to reveal this collected information to users, these often present an incomplete view of the information being collected and of how it is used for targeting ads, thus necessitating further transparency.

In this paper, we describe a novel transparency mechanism that can force transparency upon online advertising platforms: transparency-enhancing advertisements (Treads), which we define as targeted advertisements where the advertiser reveals information about their targeting to the end user. We envision that Treads would allow third-party organizations to act as transparency providers, by allowing users to opt-in and then targeting them with Treads. Through this process, users will have their platform-collected information revealed to them, but the transparency provider will not learn any more information than they would by running a normal ad. We demonstrate the feasibility of Treads by playing the role of a transparency provider: running Facebook ads targeting one of the authors and revealing partner data that Facebook hides from users but provides to advertisers (e.g., net worth). Overall, we believe that Treads can tilt the balance of power back towards users in terms of transparency of advertising platforms, and open promising new avenues for transparency in online advertising.