In this study, the German "Corona-Warn-App" of the German Federal Government and the Robert-Koch-Institute is examined by means of a non-representative online survey with 1482 participants for reasons of use and non-use. The study provides insights into user behavior with the app during the Corona pandemic, highlights the topic of data protection and how the app is used in general. Our results show that the app is often not used due to privacy concerns, but that there are also technical problems and doubts about its usefulness. In addition, the app is mainly used due to altruistic reasons and is often opened to view the own risk assessment and to ensure its functionality. To better understand the results, we compare our results with a sample of infas 360 with 10553 participants. It is shown that the results of this study can be compared to a larger population. Finally, the results are discussed and recommendations for action are derived.