Searcharxiv⌕ Search

arXiv subjects

Cristiana Santos

Publications and source records attributed to Cristiana Santos.

At least 19 recordsLinked to original sources
arXiv2026

The TCF doesn't really A(A)ID -- Automatic Privacy Analysis and Legal Compliance of TCF-based Android Applications

The Transparency and Consent Framework (TCF), developed by the Interactive Advertising Bureau (IAB) Europe, provides a de facto standard for requesting, recording, and managing user consent from European end-users. This framework has previously been found to infringe European data protection law and has subsequently been regularly updated. Previous research on the TCF focused exclusively on web contexts, with no attention given to its implementation in mobile applications. No work has systematically studied the privacy implications of the TCF on Android apps. To address this gap, we investigate the prevalence of the TCF in popular Android apps from the Google Play Store, and assess whether these apps respect users' consent banner choices. By scraping and downloading 4482 of the most popular Google Play Store apps on an emulated Android device, we automatically determine which apps use the TCF, automatically interact with consent banners, and analyze the apps' traffic in two different stages, passive (post choices) and active (during banner interaction and post choices). We found that 576 (12.85%) of the 4482 downloadable apps in our dataset implemented the TCF, and we identified potential privacy violations within this subset. In 15 (2.6%) of these apps, users' choices are stored only when consent is granted. Users who refuse consent are shown the consent banner again each time they launch the app. Network traffic analysis conducted during the passive stage reveals that 66.2% of the analyzed TCF-based apps share personal data, through the Android Advertising ID (AAID), in the absence of a lawful basis for processing. 55.3% of apps analyzed during the active stage share AAID before users interact with the apps' consent banners, violating the prior consent requirement.

cs.CR↗
arXiv2025

"I need to learn better searching tactics for privacy policy laws." Investigating Software Developers' Behavior When Using Sources on Privacy Issues

Since the introduction of the European General Data Protection Regulation (GDPR) and the California Consumer Privacy Act (CCPA), software developers increasingly have to make privacy-related decisions during system design and implementation. However, past research showed that they often lack legal expertise and struggle with privacy-compliant development. To shed light on how effective current information sources are in supporting them with privacy-sensitive implementation, we conducted a qualitative study with 30 developers. Participants were presented with a privacy-sensitive scenario and asked to identify privacy issues and suggest measures using their knowledge, online resources, and an AI assistant. We observed developers' decision-making in think-aloud sessions and discussed it in follow-up interviews. We found that participants struggled with all three sources: personal knowledge was insufficient, web content was often too complex, and while AI assistants provided clear and user-tailored responses, they lacked contextual relevance and failed to identify scenario-specific issues. Our study highlights major shortcomings in existing support for privacy-related development tasks. Based on our findings, we discuss the need for more accessible, understandable, and actionable privacy resources for developers.

cs.SE↗
arXiv2025

"I will never pay for this" Perception of fairness and factors affecting behaviour on 'pay-or-ok' models

The rise of cookie paywalls ('pay-or-ok' models) has prompted growing debates around the right to privacy and data protection, monetisation, and the legitimacy of user consent. Despite their increasing use across sectors, limited research has explored how users perceive these models or what shapes their decisions to either consent to tracking or pay. To address this gap, we conducted four focus groups (n= 14) to examine users' perceptions of cookie paywalls, their judgments of fairness, and the conditions under which they might consider paying, alongside a legal analysis within the EU data protection legal framework. Participants primarily viewed cookie paywalls as profit-driven, with fairness perceptions varying depending on factors such as the presence of a third option beyond consent or payment, transparency of data practices, and the authenticity or exclusivity of the paid content. Participants voiced expectations for greater transparency, meaningful control over data collection, and less coercive alternatives, such as contextual advertising or "reject all" buttons. Although some conditions, including trusted providers, exclusive content, and reasonable pricing, could make participants consider paying, most expressed reluctance or unwillingness to do so. Crucially, our findings raise concerns about economic exclusion, where privacy and data protection might end up becoming a privilege rather than fundamental rights. Consent given under financial pressure may not meet the standard of being freely given, as required by the GDPR. To address these concerns, we recommend user-centred approaches that enhance transparency, reduce coercion, ensure the value of paid content, and explore inclusive alternatives. These measures are essential for supporting fairness, meaningful choice, and user autonomy in consent-driven digital environments.

cs.CY↗
arXiv2025

Turning to Online Forums for Legal Information: A Case Study of GDPR's Legitimate Interests

Practitioners building online services and tools often turn to online forums such as Reddit, Law Stack Exchange, and Stack Overflow for legal guidance to ensure compliance with the GDPR. The legal information presented in these forums directly impacts present-day industry practitioner's decisions. Online forums can serve as gateways that, depending on the accuracy and quality of the answers provided, may either support or undermine the protection of privacy and data protection fundamental rights. However, there is a need for deeper investigation into practitioners' decision-making processes and their understanding of legal compliance when seeking for legal information online. Using GDPR's ``legitimate interests'' legal ground for processing personal data as a case study, we investigate how practitioners use online forums to identify common areas of confusion in applying legitimate interests in practice, and evaluate how legally sound online forum responses are. Our analysis found that applying the legal basis of legitimate interest is complex for practitioners, with important implications for how the GDPR is implemented in practice. The legal analysis showed that crowdsourced legal information tends to be legally sound, though sometimes incomplete. We outline recommendations to improve the quality of online forums by ensuring that responses are more legally sound and comprehensive, enabling practitioners to apply legitimate interests effectively in practice and uphold the GDPR.

cs.CY↗
arXiv2025

You Can't Trust Your Tag Neither: Privacy Leaks and Potential Legal Violations within the Google Tag Manager

Tag Management Systems were developed in order to support website publishers in installing multiple third-party JavaScript scripts (Tags) on their websites. Google developed its own TMS called ``Google Tag Manager'' (GTM) that is currently present on 42\% of the top 1 million most popular websites. However, GTM has not yet been thoroughly evaluated by the academic research community. In this work, we study, for the first time, the Tags provided within the GTM system. We propose a new methodology called ``detecting privacy leaks in isolation'' and apply it to multiple Tags to analyse the types of data that Tags collect and contrast them to the legal and technical documentation, in collaboration with a legal expert. Across three studies - in-depth analysis of 6 Tags, automated analysis of 718 Tags, and analysis of Google ``Consent Mode'' - we discover multiple hidden data leaks, incomplete and diverging declarations, undisclosed third-parties and cookies, personal data sharing without consent and we further identify potential legal violations within EU Data Protection law.

cs.CR↗
arXiv2025

Measuring Compliance of Consent Revocation on the Web

The GDPR requires websites to facilitate the right to revoke consent from Web users. While numerous studies measured compliance of consent with the various consent requirements, no prior work has studied consent revocation on the Web. Therefore, it remains unclear how difficult it is to revoke consent on the websites' interfaces, nor whether revoked consent is properly stored and communicated behind the user interface. Our work aims to fill this gap by measuring compliance of consent revocation on the Web on the top-200 websites. We found that 19.87% of websites make it difficult for users to revoke consent throughout different interfaces, 20.5% of websites require more effort than acceptance, and 2.48% do not provide consent revocation at all, thus violating legal requirements for valid consent. 57.5% websites do not delete the cookies after consent revocation enabling continuous illegal processing of users' data. Moreover, we analyzed 281 websites implementing the IAB Europe TCF, and found 22 websites that store a positive consent despite user's revocation. Surprisingly, we found that on 101 websites, third parties that have received consent upon user's acceptance, are not informed of user's revocation, leading to the illegal processing of users' data by such third parties. Our findings emphasise the need for improved legal compliance of consent revocation, and proper, consistent, and uniform implementation of revocation communication and data deletion practices.

cs.CR↗
arXiv2024

"It doesn't tell me anything about how my data is used'': User Perceptions of Data Collection Purposes

Data collection purposes and their descriptions are presented on almost all privacy notices under the GDPR, yet there is a lack of research focusing on how effective they are at informing users about data practices. We fill this gap by investigating users' perceptions of data collection purposes and their descriptions, a crucial aspect of informed consent. We conducted 23 semi-structured interviews with European users to investigate user perceptions of six common purposes (Strictly Necessary, Statistics and Analytics, Performance and Functionality, Marketing and Advertising, Personalized Advertising, and Personalized Content) and identified elements of an effective purpose name and description. We found that most purpose descriptions do not contain the information users wish to know, and that participants preferred some purpose names over others due to their perceived transparency or ease of understanding. Based on these findings, we suggest how the framing of purposes can be improved toward meaningful informed consent.

cs.HC↗
arXiv2023

Legitimate Interest is the New Consent -- Large-Scale Measurement and Legal Compliance of IAB Europe TCF Paywalls

Cookie paywalls allow visitors of a website to access its content only after they make a choice between paying a fee or accept tracking. European Data Protection Authorities (DPAs) recently issued guidelines and decisions on paywalls lawfulness, but it is yet unknown whether websites comply with them. We study in this paper the prevalence of cookie paywalls on the top one million websites using an automatic crawler. We identify 431 cookie paywalls, all using the Transparency and Consent Framework (TCF). We then analyse the data these paywalls communicate through the TCF, and in particular, the legal grounds and the purposes used to collect personal data. We observe that cookie paywalls extensively rely on legitimate interest legal basis systematically conflated with consent. We also observe a lack of correlation between the presence of paywalls and legal decisions or guidelines by DPAs.

cs.CY↗
arXiv2023

An Ontology of Dark Patterns Knowledge: Foundations, Definitions, and a Pathway for Shared Knowledge-Building

Deceptive and coercive design practices are increasingly used by companies to extract profit, harvest data, and limit consumer choice. Dark patterns represent the most common contemporary amalgamation of these problematic practices, connecting designers, technologists, scholars, regulators, and legal professionals in transdisciplinary dialogue. However, a lack of universally accepted definitions across the academic, legislative and regulatory space has likely limited the impact that scholarship on dark patterns might have in supporting sanctions and evolved design practices. In this paper, we seek to support the development of a shared language of dark patterns, harmonizing ten existing regulatory and academic taxonomies of dark patterns and proposing a three-level ontology with standardized definitions for 65 synthesized dark patterns types across low-, meso-, and high-level patterns. We illustrate how this ontology can support translational research and regulatory action, including pathways to extend our initial types through new empirical work and map across application domains.

cs.HC↗
arXiv2022

Your Consent Is Worth 75 Euros A Year -- Measurement and Lawfulness of Cookie Paywalls

Most websites offer their content for free, though this gratuity often comes with a counterpart: personal data is collected to finance these websites by resorting, mostly, to tracking and thus targeted advertising. Cookie walls and paywalls, used to retrieve consent, recently generated interest from EU DPAs and seemed to have grown in popularity. However, they have been overlooked by scholars. We present in this paper 1) the results of an exploratory study conducted on 2800 Central European websites to measure the presence and practices of cookie paywalls, and 2) a framing of their lawfulness amidst the variety of legal decisions and guidelines.

cs.CY↗
arXiv2021

Cookie Banners, What's the Purpose? Analyzing Cookie Banner Text Through a Legal Lens

A cookie banner pops up when a user visits a website for the first time, requesting consent to the use of cookies and other trackers for a variety of purposes. Unlike prior work that has focused on evaluating the user interface (UI) design of cookie banners, this paper presents an in-depth analysis of what cookie banners say to users to get their consent. We took an interdisciplinary approach to determining what cookie banners should say. Following the legal requirements of the ePrivacy Directive (ePD) and the General Data Protection Regulation (GDPR), we manually annotated around 400 cookie banners presented on the most popular English-speaking websites visited by users residing in the EU. We focused on analyzing the purposes of cookie banners and how these purposes were expressed (e.g., any misleading or vague language, any use of jargon). We found that 89% of cookie banners violated applicable laws. In particular, 61% of banners violated the purpose specificity requirement by mentioning vague purposes, including "user experience enhancement". Further, 30% of banners used positive framing, breaching the freely given and informed consent requirements. Based on these findings, we provide recommendations that regulators can find useful. We also describe future research directions.

cs.HC↗
arXiv2021

Why IP-based Subject Access Requests Are Denied?

Understanding the legal status of IP addresses is complex. In Europe, the General Data Protection Regulation (GDPR) is supposed to have leveraged the legal status of IP addresses as personal data, but recent decisions from the European Court of Justice undermine this view. In the hope to clarify this situation, we have looked on how 109 websites deal with IP addresses. First, we analyzed the privacy policies of these websites to determine how they considered IP addresses. Most of them acknowledge in their privacy policy the fact that IP addresses are personal data. Second, we submitted subject access requests based on the IP addresses used to visit different websites. Our requests were often denied. Websites justify their answers with different explanations suchlike: you need to register, or IP addresses do not allow to identify you, to name a few. This situation is rather frustrating for any user wanting to exercise his/her rights: IP addresses are personal data on (legal) papers, but there are no means to exercise the rights thereto. One maybe tempted to say that IP addresses are not personal data. We make several proposals to improve this situation by modifying how IP addresses are allocated to a user.

cs.CR↗
arXiv2021

Did I delete my cookies? Cookies respawning with browser fingerprinting

Stateful and stateless web tracking gathered much attention in the last decade, however they were always measured separately. To the best of our knowledge, our study is the first to detect and measure cookie respawning with browser and machine fingerprinting. We develop a detection methodology that allows us to detect cookies dependency on browser and machine features. Our results show that 1,150 out of the top 30, 000 Alexa websites deploy this tracking mechanism. We further uncover how domains collaborate to respawn cookies through fingerprinting. We find out that this technique can be used to track users across websites even when third-party cookies are deprecated. Together with a legal scholar, we conclude that cookie respawning with browser fingerprinting lacks legal interpretation under the GDPR and the ePrivacy directive, but its use in practice may breach them, thus subjecting it to fines up to 20 million euro.

cs.CR↗
arXiv2021

Consent Management Platforms under the GDPR: processors and/or controllers?

Consent Management Providers (CMPs) provide consent pop-ups that are embedded in ever more websites over time to enable streamlined compliance with the legal requirements for consent mandated by the ePrivacy Directive and the General Data Protection Regulation (GDPR). They implement the standard for consent collection from the Transparency and Consent Framework (TCF) (current version v2.0) proposed by the European branch of the Interactive Advertising Bureau (IAB Europe). Although the IAB's TCF specifications characterize CMPs as data processors, CMPs factual activities often qualifies them as data controllers instead. Discerning their clear role is crucial since compliance obligations and CMPs liability depend on their accurate characterization. We perform empirical experiments with two major CMP providers in the EU: Quantcast and OneTrust and paired with a legal analysis. We conclude that CMPs process personal data, and we identify multiple scenarios wherein CMPs are controllers.

cs.HC↗
arXiv2021

Dark Patterns and the Legal Requirements of Consent Banners: An Interaction Criticism Perspective

User engagement with data privacy and security through consent banners has become a ubiquitous part of interacting with internet services. While previous work has addressed consent banners from either interaction design, legal, and ethics-focused perspectives, little research addresses the connections among multiple disciplinary approaches, including tensions and opportunities that transcend disciplinary boundaries. In this paper, we draw together perspectives and commentary from HCI, design, privacy and data protection, and legal research communities, using the language and strategies of "dark patterns" to perform an interaction criticism reading of three different types of consent banners. Our analysis builds upon designer, interface, user, and social context lenses to raise tensions and synergies that arise together in complex, contingent, and conflicting ways in the act of designing consent banners. We conclude with opportunities for transdisciplinary dialogue across legal, ethical, computer science, and interactive systems scholarship to translate matters of ethical concern into public policy.

cs.HC↗
arXiv2020

Are cookie banners indeed compliant with the law? Deciphering EU legal requirements on consent and technical means to verify compliance of cookie banners

In this work, we analyze the legal requirements on how cookie banners are supposed to be implemented to be fully compliant with the e-Privacy Directive and the General Data Protection Regulation. Our contribution resides in the definition of seventeen operational and fine-grained requirements on cookie banner design that are legally compliant, and moreover, we define whether and when the verification of compliance of each requirement is technically feasible. The definition of requirements emerges from a joint interdisciplinary analysis composed of lawyers and computer scientists in the domain of web tracking technologies. As such, while some requirements are provided by explicitly codified legal sources, others result from the domain-expertise of computer scientists. In our work, we match each requirement against existing cookie banners design of websites. For each requirement, we exemplify with compliant and non-compliant cookie banners. As an outcome of a technical assessment, we verify per requirement if technical (with computer science tools) or manual (with any human operator) verification is needed to assess compliance of consent and we also show which requirements are impossible to verify with certainty in the current architecture of the Web. For example, we explain how the requirement for revocable consent could be implemented in practice: when consent is revoked, the publisher should delete the consent cookie and communicate the withdrawal to all third parties who have previously received consent. With this approach we aim to support practically-minded parties (compliance officers, regulators, researchers, and computer scientists) to assess compliance and detect violations in cookie banner design and implementation, specially under the current revision of the European Union e-Privacy framework.

cs.CR↗
arXiv2020

Artificial intelligence in space

In the next coming years, space activities are expected to undergo a radical transformation with the emergence of new satellite systems or new services which will incorporate the contributions of artificial intelligence and machine learning defined as covering a wide range of innovations from autonomous objects with their own decision-making power to increasingly sophisticated services exploiting very large volumes of information from space. This chapter identifies some of the legal and ethical challenges linked to its use. These legal and ethical challenges call for solutions which the international treaties in force are not sufficient to determine and implement. For this reason, a legal methodology must be developed that makes it possible to link intelligent systems and services to a system of rules applicable thereto. It discusses existing legal AI-based tools amenable for making space law actionable, interoperable and machine readable for future compliance tools.

cs.CY↗