Many websites contain services from third parties. Misconfigurations of these services can lead to missing compliance with legal obligations and privacy risks for website users. Previous research indicates that one cause for such privacy issues is missing awareness. However, reasons for the missing awareness and other reasons for the prevalence of privacy issues are not widely researched; that includes website owners’ dealing with those issues. To shed light on the issue, we analyze 1043 responses from website owners to a notification about a privacy issue on their website using thematic analysis, following an exploratory and qualitative approach. Our analysis shows that, next to unawareness of the issue, incorrect technical implementation and ambiguous responsibilities are among the reasons for privacy issues. Also, website owners face different challenges, such as a lack of knowledge or slow organizational coordination and processes. In addition, our results show that the circumstances in which they operate their website influences how they act and what challenges they face. To illustrate these differences in website owners, we derive three personas from our thematic analysis: (1) the Ignorant Hobbyist, (2) the Busy Self-Employed, and (3) the Informed Multi-Stakeholder. These personas cover the majority of the aspects of the analyzed responses and represent the diversity of website owners and their backgrounds. Given the challenges and backgrounds of website owners, we discuss which prerequisites must be fulfilled to remediate privacy issues on websites. Finally, we present measures that support website owners in remediating privacy issues and show how to adapt these measures to the needs of different website owners. We hope that better support for website owners will also lead to better privacy for website visitors.

Researchers help operators of vulnerable and non-compliant internet services by individually notifying them about security and privacy issues uncovered in their research. To improve efficiency and effectiveness of such efforts, dedicated notification studies are imperative. As of today, there is no comprehensive documentation of pitfalls and best practices for conducting such notification studies, which limits validity of results and impedes reproducibility. Drawing on our experience with such studies and guidance from related work, we present a set of guidelines and practical recommendations, including initial data collection, sending of notifications, interacting with the recipients, and publishing the results. We note that future studies can especially benefit from extensive planning and automation of crucial processes, i. e., activities that take place well before the first notifications are sent.

DNS over TLS (DoT) and DNS over HTTPS (DoH) promise to improve privacy and security of DNS by encrypting DNS messages, especially when messages are padded to a uniform size. Firstly, to demonstrate the limitations of recommended padding approaches, we present Segram, a novel app fingerprinting attack that allows adversaries to infer which mobile apps are executed on a device. Secondly, we record traffic traces of 118 Android apps using 10 differnet DoT/DoH resolvers to study the effectiveness of Segram under different conditions. According to our results, Segram identifies apps with accuracies of up to 72 % with padding in a controlled closed world setting. The effectiveness of Segram is comparable with state-of-the-art techniques but Segram requires less computational effort. We release our datasets and code. Thirdly, we study the prevalence of padding among privacy-focused DoT/DoH resolvers, finding that up to 81 % of our sample fail to enable padding. Our results suggest that recommended padding approaches are less effective than expected and that resolver operators are not sufficiently aware about this feature.