The necessity of a lab course on computer security arises from the students? need to complement course work by hands-on experience. In order to meet the distance teaching demands of our institution, we designed an internet-based laboratory. We sketch the types of tasks the students are to perform, and our approach to check immediately whether students have completed a task. Yet, the typical tasks in labs only cover work done alone, while security engineering often comprises tasks involving several independent parties. This in turn calls for collaborative tasks, which we sketch. As students operate in larger groups, and the server hosting the lab machines can only run a finite number of them simultaneously, a reservation scheme is employed to guarantee fair access for all participants.