In this talk I will outline how the theory of Quantitative Information Flow which was developed to provide a rigorous framework to measure information leakage was used to probe the Brazilian Education Censuses. Using this theory applied to these datasets showed that the defences proposed by the Ministry were prone to serious vulnerabilities, in some cases leading to complete re-identification under reasonably modest attacks. The consequence is that our work has provided the agency with rigorously formalized risk analysis, which will help it make informed decisions.