The NetFlow Visualizer (NFVis) is a part of the solution in network security domain provided by Mycroft Mind, a.s. company. This tool is so called proof-of-concept tool and provides new type of visualization of the NetFlow data. Communication on the network is visualized as a graph where nodes are network devices and transfers between these devices are represented as directed edges. Unlike other tools the NetFlow Visualizer is able to focus on details. It is able to seek and explore each individual data transfer.