Rapid evolution of numerous types of sensors and communicating objects has significantly enhanced the content of information systems, especially mobile ones. However, it raises new questions about trust one can have in information and sources. Indeed, sources can be duped or under external control falsifying source's information. This paper proposes to study security of information systems through the notion of trust. First, definition then evaluation of trust in heterogeneous networks are introduced. Afterwards, we propose modelling of sources. Trust in sources is studied and measured through two characteristics: competence and sincerity. Experiments based on several simulated sources from a real dataset show the relevance of our approach. This work is applied to the analysis of position and navigation data.