Driven by use case scenarios, WP5 aims to evaluate the results obtained in WP 2 (Policy and Transparency Framework), WP 3 (Big Data Policy Engine), and WP 4 (User Interaction) under conditions. More specifically, the goal of T5.3 Public challenges is to expose the developed system and its components to public hacking challenges, which would, together with the internal backend scalability and robustness testing performed in WP3 (D3.3 and D3.5) and frontend testing in WP4 (D4.2 and D4.4), provide the necessary feedback for further development of the SPECIAL platform. To guarantee the robustness of our architecture, such tests must focus on ensuring that both the individual components and the infrastructure as a whole are capable of sharing data only with authorized parties, while guaranteeing that policies and regulations are being adhered to. This means that the challenges should span beyond just penetration testing, and involve other aspects of the system, be it technical or legal, highlighting any limitations. Moreover, WP 6 (Collaboration, Dissemination & Standardisation) will organize public workshops to present and discuss such limitations and obtain input with respect to possible additional challenges. The experiences gained from all these activities will be merged, generalized, and translated into a set of methodological guidelines for future implementations.