Ransomware is a type of advanced malware that has spread rapidly in recent years, causing significant financial losses for a wide range of victims including organizations, healthcare facilities, and individuals. Modern host-based detection methods require the host to be infected first in order to identify anomalies and detect the malware. By the time of infection, it can be too late as some of the system’s assets would have been already exfiltrated or encrypted by the malware. Conversely, network-based methods can be effective in detecting ransomware attacks, as most ransomware families try to connect to command and control servers before their harmful payloads are executed. Therefore, a careful analysis of ransomware network traffic can be one of the key means for early detection. This paper demonstrates a comprehensive behavioral analysis of crypto ransomware network activities, taking Locky, one of the most serious families, as a case study. A dedicated testbed was built, and a set of valuable and informative network features were extracted and classified into multiple types. A network-based intrusion detection system was implemented, employing two independent classifiers working in parallel on different levels: packet and flow levels. Experimental evaluation of the proposed detection system demonstrates that it offers high detection accuracy, low false positive rate, valid extracted features, and is highly effective in tracking ransomware network activities.