Can we trust ICT (Information & Communication Technology) systems? Every single day a handful of previously unknown security vulnerabilities on these environments are published, dangerously feeding the lack of trust feeling that many end users already exhibit with respect to ICT. In order to disrupt and even invert such a perilous tendency (hindering the wide adoption of ICT and all its associated benefits), a number of research challenges in the field of cyber security need to be addressed. This paper presents some of these key challenges, offering initial thoughts on how to tackle each of them.