The purpose of this study is to help Internet users to adopt and maintain a healthy lifestyle, it is imperative to increase self-management competencies to improve healthy eating and regular physical activity. Aim of this research project is to evaluate an evidence- and theory-based computerized expert system in comparison to a standard program. In addition, two different tailoring criteria are compared to each other with regard to the misclassification of study participants. Internet users will be treated psychologically and followed up over 12 weeks. The computerized expert system is expected to help users better than the standard program. Both interventions are hypothesized to improve self-management competencies over time.