The security of computer networks has become a priority during the past few years. More and more organizations heavily depend on services that are provided by computer networks and this trend is certainly going to rise in the near future. At the same time, malicious attacks against such systems are also increasing in number and variety. System administrators can try to prevent these attacks with the use of firewalls for instance. However, these precautions are not always enough and so they also need to monitor the network traffic in order to detect anomalies and intrusions. Usually, system administrators use automated systems to process network traffic logs and to analyze them. This processing is based on learning techniques, signature databases or statistical analysis. Another approach is to use visualization techniques to display these logs and to favor user interaction with the data. This paper presents a visualization design based on interactive grids representing the network space. The network traffic is then displayed on these grids. We also introduce a prototype of this design that has been implemented to test its validity.