Network scans are very common and frequent events that appear in almost every network. Generally, the scans are quite harmless. Scanning can be useful for network operators, who need to know state of their infrastructures. Contrary, scans can be used also for gathering sensitive information by attackers. This paper describes a simple detection method that was used to detect vertical scans. Our aim is to show results of long-term measurement on backbone network and to show that it is possible to detect scans efficiently even with a simple method. The paper presents several interesting statistics that characterize network behavior and scanning frequency in a large high-speed national academic network.