The Information Society is increasingly dependent on largely distributed systems and infrastructures for life-critical and business-critical functions. The complexity of systems in Information Society is rapidly growing because of a number of factors like their size, their unboundness and interdependency, the multiplicity of involved actors, the need to pursue more decentralised control and, last but not least, the growing sophistication in functionality. This trend together with the pervasive use both of open information infrastructures for communications as well as of freeware software and common application platforms expose our society to new cyber vulnerabilities and threats that deserve better understanding, assessment and control. Building trust is essential for the development of the Information Society, and the electronic commerce in particular. This paper outlines the main research directions that have been defined as the priority ones in which to engage the European research community in the thematic priority Information Society Technologies (IST) of the 6th Framework Programme. To this purpose, the paper consolidates the results and recommendations of a number of consultation Workshops that were organised by the Commission in the years 2000-2002.