With the increased performance of large language models (LLMs), conversational agents (CA), such as ChatGPT, are nowadays available to any individual requiring little technical knowledge and skills. Initial studies that have investigated related privacy risks primarily focused on either technical aspects and misuse of these tools, or captured overall perceptions of CA users in small-scale qualitative evaluations. Complementing and extending previous work, we used a quantitative user-centered approach to analyze and compare the behaviors and concerns of users and non-users. We conducted a survey study (N=422) with (1) service users, i.e., users of CA services, (2) local users, i.e., users of a local instance of CA (partially local users, or fully local users), and (3) non-users. We collected self-reported usage patterns and personal data-sharing behavior as well as privacy concerns related to different types of personal data (e.g., health data, demographics, or opinions). Furthermore, we analyze individuals' intention to use CA services in multiple scenarios. Our findings show that users of CA services generally have fewer privacy concerns than non-users. While users rarely share data related to personal identifiers and account credentials, they tend to often share data related to lifestyle, health, standard of living, and opinions. Surprisingly, partially local users tend to share more data with CA services as they also generally use CA services more often and for more diverse purposes. Also, while the majority of CA services users declared not being willing to prioritize CA services as an information source in the described scenarios such as seeking legal advice, between about one-quarter and one-third of partially local users would use CA services for all scenarios. Furthermore, half of the users were willing to stop using CA for privacy reasons (e.g., in case of data leaks), whereas a large majority of non-users reported not using CAs simply because they do not have the need or the opportunity. Our work highlights the high privacy risks for CA services users as CA services largely expand the amount of any type of personal information that can be collected by companies.

Wearable activity trackers (WATs) have recently gained worldwide popularity, with over a billion devices collecting a range of personal data. To receive additional services, users commonly share this data with third-party applications (TPAs). However, this practice poses potential privacy risks. Privacy-enhancing technologies have been developed to address these concerns, but they often lack user-centered design, and therefore, are less likely to be directly related to users' concerns and to be widely adopted. This study takes a participatory design approach involving N=26 experienced WAT users who share data with TPAs. Through a series of design sessions, participants conceptualized 19 solutions, from which we identified seven different design features. We further analyze and discuss how these features can be combined to assist users in managing their data sharing with TPAs and, therefore, enhancing their privacy. Finally, we selected the three most promising features, namely partial sharing, reminder, and revocation assistance, and conducted an online survey with N=201 WAT users to better understand the potential effectiveness and usability of these features. This work makes an important contribution by offering user-centered solutions and valuable insights for integrating privacy-enhancing technologies into the WAT ecosystem.

The number of users of wearable activity trackers (WATs) has rapidly increased over the last decade. Although these devices enable their users to monitor their activities and health, they also raise new security and privacy concerns, given the sensitive data (e.g., steps, heart rate) they collect and the information that can be inferred from this data (e.g., diseases). In addition to sharing with the service providers (e.g., Fitbit), WAT users can share their fitness data with third-party applications (TPAs) and individuals. Understanding how and with whom users share their fitness data and what kind of approaches they take to preserve their privacy are key to assessing the underlying privacy risks and to further designing appropriate privacy-enhancing techniques. In this work, we perform, through a large-scale survey of N=628 WAT users, the first quantitative and qualitative analysis of users' awareness, understanding, attitudes, and behaviors toward fitness-data sharing with TPAs and individuals. By asking these users to draw their thoughts, we explore, in particular, users' practices and actual behaviors toward fitness-data sharing and their mental models. Our empirical results show that about half of WAT users underestimate the number of TPAs to which they have granted access to their data, and 63% share data with at least one TPA that they do not actively use (anymore). Furthermore, 29% of the users do not revoke TPA access to their data because they forget they gave access to it in the first place, and 8% were not even aware they could revoke access to their data. Finally, their mental models, as well as some of their answers, demonstrate substantial gaps in their understanding of the data-sharing process. Importantly, 67% of the respondents think that TPAs cannot access the fitness data that was collected before they granted access to it, whereas TPAs actually can do this.