Recently, observed cyber-attacks have been often triggered by “malwares” and have been maliciously evolving and sometimes hidden from our monitoring countermeasures (FW, IDS/IPS). For achieving advanced security solution, utilizing passive monitoring technologies should be considered. In this presentation, passive monitoring technologies such as darknet and honeypot/sandbox are explained with practical use-cases to accurately observe and monitor ongoing threats (cyber-attacks). The use-cases may include detection of malware-infected IoT devices by means of darknet and honeypot monitoring. Furthermore, detection of cyber-attacks by passive monitoring can be utilized for cyber security proactive response as practical solutions.