The data is solely stored at the three universities Münster, Bonn and Duisburg-Essen and is therefore protected by the strict German Data Privacy Act (Datenschutzgesetz). The access is SSL encrypted.
Please be aware that sciebo is not built for the handling of personal data and as such should not be used to store sensible data.
The terms of service for the university use of the sciebo service can be found here.
You can find further information in the sciebo terms of service.