We present the design and a prototype of a lab course on computer security, the necessity of which arises from the students' need to complement course work by hands-on experience. In order to guarantee maintainability of a number of Linux systems on which students change configurations, we decided to employ a virtual machine approach. This allows to reset configurations quickly without another costly operating system installation. We sketch the types of tasks the students are to perform, and our approach to check immediately whether students have completed a task. As students operate in larger groups, and the server hosting the virtual machines can only run a finite number of them simultaneously, a reservation scheme is employed to guarantee fair access for all participants. KEY WORDS Education, remote laboratory, resource sharing, IT-security, virtualization, semi-automatic assessment