Malwares are spread all over cyberspace and often lead to serious security incidents. To grasp the present trends of malware activities, there are a number of ongoing network monitoring projects that collect large amount of data such as network traffic and IDS logs. These data need to be analyzed in depth since they potentially contain critical symptoms, such as an outbreak of new malware, a stealthy activity of botnet and a new type of attack on unknown vulnerability, etc. We have been developing the Network Incident analysis Center for Tactical Emergency Response (NICTER), which monitors a wide range of networks in real-time. The NICTER deploys several analysis engines taking advantage of data mining techniques in order to analyze the monitored traffics. This paper describes a brief overview of the NICTER, and its data mining based analysis engines, such as Change Point Detector (CPD), Self-Organizing Map analyzer (SOM analyzer) and Incident Forecast engine (IF).