" Your hashed IP address: Ubuntu. ": perspectives on transparency tools for online advertising.

Ad personalization has been criticized in the past for invading privacy, lack of transparency, and improper controls offered to users. Recently, companies started to provide web portals and other means for users to access data collected about them. In this paper, we study these new transparency tools from multiple perspectives using a mixed-methods approach. Still practices of data sharing barely changed until recently when new legislation required all companies to grant individual access to personal data stored about them. Using a mixed-methods approach we study the benefits of the new rights for users. First, we analyze transparency tools provided by 22 companies and check whether they follow previous recommendations for usability and user expectations. Based on these insights, we conduct a survey with 490 participants to evaluate three common approaches to disclose data. To complement this user-centric view, we shed light on the design decisions and complexities of transparency in online advertising using an online survey (n = 24) and in-person interviews (n = 8) with experts from the industry. We find that newly created transparency tools present a variety of information to users, from detailed technical logs to high-level interest segment information. Our results indicate that users do not (yet) know what to learn from the data and mistrust the accuracy of the information shown to them. At the same time, new transparency requirements pose several challenges to an industry that excessively shares data that even they sometimes cannot relate to an individual.