  Capture the Flag games represent a popular method of cybersecurity training.
Providing meaningful insight into the training progress is essential for
increasing learning impact and supporting participants' motivation, especially
in advanced hands-on courses. In this paper, we investigate how to provide
valuable post-game feedback to players of serious cybersecurity games through
interactive visualizations. In collaboration with domain experts, we formulated
user requirements that cover three cognitive perspectives: gameplay overview,
person-centric view, and comparative feedback. Based on these requirements, we
designed two interactive visualizations that provide complementary views on
game results. They combine a known clustering and time-based visual approaches
to show game results in a way that is easy to decode for players. The
purposefulness of our visual feedback was evaluated in a usability field study
with attendees of the Summer School in Cyber Security. The evaluation confirmed
the adequacy of the two visualizations for instant post-game feedback. Despite
our initial expectations, there was no strong preference for neither of the
visualizations in solving different tasks.
