Mobile devices are an interesting opportunity to collect a wide range of valuable health data for both care and research, such as questionnaire data, measurements (heartrate, blood pressure), distance travelled and other sensor information. In the LUMC various healthcare apps have been developed, for example the Woundcare app for determining if a surgery wound may become infected after surgery and the Participatient app that aims to reduce catheter infections. The data collected by these apps is highly privacy sensitive and requires special protection. Securing the data by pseudonymization, that means replacing identifying information with codes, is an important security measure.