Tools for Achieving Usable Ex Post Transparency: A Survey <s> c: ICONS <s> The rapid adoption of location tracking and mobile social networking technologies raises significant privacy challenges. Today our understanding of people's location sharing privacy preferences remains very limited, including how these preferences are impacted by the type of location tracking device or the nature of the locations visited. To address this gap, we deployed Locaccino, a mobile location sharing system, in a four week long field study, where we examined the behavior of study participants (n=28) who shared their location with their acquaintances (n=373.) Our results show that users appear more comfortable sharing their presence at locations visited by a large and diverse set of people. Our study also indicates that people who visit a wider number of places tend to also be the subject of a greater number of requests for their locations. Over time these same people tend to also evolve more sophisticated privacy preferences, reflected by an increase in time- and location-based restrictions. We conclude by discussing the implications our findings. <s> BIB001 </s> Tools for Achieving Usable Ex Post Transparency: A Survey <s> c: ICONS <s> Today's rich service offer in the World Wide Web increasingly requires the disclosure of personal user data. Service providers' appetite for personal user data, however, is accompanied by growing privacy implications for Internet users. Addressing this rising threat, privacy-enhancing technologies aim at aiding users in protecting their personal data. Even though effective privacy laws facilitate users to edit and revoke already disclosed personal data, few PET solutions support users in exercising this right. Available tools lack intuitive interfaces and are built on powerful infrastructures on the provider side. In this paper we introduce the Data Disclosure Log component within a user-centric privacy architecture. Built on a browser-based logging extension, we present a visualization tool that displays past personal data disclosures from different perspectives. A graph-based view allows for the dynamic presentation of relations between selected entity types. Such an overview enables users to know the conditions of past personal data transactions at any time. This knowledge represents a prerequisite for an ex post revision or revocation of personal data. Usability and user acceptance of the developed prototype is evaluated in a conducted user test. <s> BIB002 </s> Tools for Achieving Usable Ex Post Transparency: A Survey <s> c: ICONS <s> A large body of research has focused on disclosure policies for controlling information release in social sharing (e.g., location-based) applications. However, less work has considered how exposed these policies actually leave users; i.e., to what extent are disclosures in compliance with these policies actually being made? For instance, consider a disclosure policy granting Alice's coworkers access to her location during work hours. Alice might feel that this policy appropriately controls her exposure, but may feel differently if she learned that her boss was accessing her location every 5 minutes. In addition to specifying who has access to personal information, users need a way to quantify, interpret, and control the extent to which this data is shared. We propose and evaluate an intuitive mechanism for summarizing and controlling a user's exposure on smartphone-based platforms. Our approach uses the visual metaphor of eyes appearing and growing in size on the home screen; the rate at which these eyes grow depends on the number of accesses granted for a user's location, and the type of person (e.g., family vs. friend) making these accesses. This approach gives users an accurate and ambient sense of their exposure and helps them take actions to limit their exposure, all without explicitly identifying the social contacts making requests. Through two systematic user studies (N = 43,41) we show that our interface is indeed effective at summarizing complex exposure information and provides comparable information to a more cumbersome interface presenting more detailed information. <s> BIB003 </s> Tools for Achieving Usable Ex Post Transparency: A Survey <s> c: ICONS <s> The ever increasing popularity of apps stems from their ability to provide highly customized services to the user. The flip side is that in order to provide such services, apps need access to very sensitive private information about the user. This leads to malicious apps that collect personal user information in the background and exploit it in various ways. Studies have shown that current app vetting processes which are mainly restricted to install time verification mechanisms are incapable of detecting and preventing such attacks. We argue that the missing fundamental aspect here is a comprehensive and usable mobile privacy solution, one that not only protects the user's location information, but also other equally sensitive user data such as the user's contacts and documents. A solution that is usable by the average user who does not understand or care about the low level technical details. To bridge this gap, we propose privacy metrics that quantify low-level app accesses in terms of privacy impact and transforms them to high-level user understandable ratings. We also provide the design and architecture of our Privacy Panel app that represents the computed ratings in a graphical user-friendly format and allows the user to define policies based on them. Finally, experimental results are given to validate the scalability of the proposed solution. <s> BIB004 </s> Tools for Achieving Usable Ex Post Transparency: A Survey <s> c: ICONS <s> We present a prototype of the user interface of a transparency tool that displays an overview of a user's data disclosures to different online service providers and allows them to access data collected about them stored at the services' sides. We explore one particular type of visualization method consisting of tracing lines that connect a user's disclosed personal attributes to the service to which these attributes have been disclosed. We report on the ongoing iterative process of design of such visualization, the challenges encountered and the possibilities for future improvements. <s> BIB005 </s> Tools for Achieving Usable Ex Post Transparency: A Survey <s> c: ICONS <s> Transparency is a basic privacy principle and social trust factor. However, in the age of cloud computing and big data, providing transparency becomes increasingly a challenge. <s> BIB006
Iconified elements and pictographs count on the recognisability of graphical symbols. Once learned, icons can be used to convey codified meaning potentially quickly. A viewer recognises icons either due to her personal experience based on previous knowledge and socio-cultural imprint, or as a result of repetitive exposure to that icon in the same application context. Ideally, icons employed by TETs would be self-descriptive and conform with the user's expectations  . If used infrequently, icons would still be recognised rather than recalled, ideally due to being standardised across multiple implementation platforms  . However, the icons discussed in the reviewed TETs are rarely universal but were found instead to be tailored to specific target audiences. Some TETs complement their textual or graphical visualisations with icons that either stem from standard icon sets VOLUME 5, 2017 FIGURE 9. Geographical heat maps by a) Biswas et al. BIB004 , and b) entropy densities by Toch et al. BIB001 . or are self explanatory enough to be recognisable in terms of their denotation (Figures 7 and 10) . Abdullah et al.  use standard folder icons to represent nodes in hierarchical structures, while Bier et al.  and Angulo et al. BIB005 use pen icons to hint at the underlying functionality of editing FIGURE 11. a) Chronological views by Fischer-Hübner et al. BIB006 , and b) by Kolter et al. BIB002 . and modifying contents. Such icons are easily recognisable by regular users of these platforms. Angulo et al. BIB005 use icons branded by online platforms to signify screen components that are related to the respective service providers, as well as individual icons for different kinds of data items. Kolter et al. BIB002 use highly customised icons to denote multiple entity types. Each type varies in colour and symbol, and each bears a textual acronym of its respective type, such as 'SP' for service provider, in the lower third of the icon (Figures 7 and 11 ). Icons that refer to online services show the branded logo of that service as an image. The primary visualisation of the TET by Schlegel et al. BIB003 relies on an iconic metaphor, a pair of eyes on the home screen of the device, to signify external queries regarding the user's location. Although the icon as such is unknown at first, its meaning becomes clearer by means of the icon's connotation, as well as by the dynamics of its appearance in correlation to the amount of disclosed data. The implementation of Hsieh et al.  makes use of a client-sided application that is used to receive local notifications. The colour of its run-time icon changes in response to the query status.