Major disturbances of large ports could lead to tremendous negative effects to maritime supply chains and the whole economy. Beside physical threats, ports are also vulnerable to cyber attacks due to their dependency on information and communications technology. Port Community Systems (PCSs) are information hubs for ports integrating information from various sources for global supply chains, connecting systems of terminal operators, carriers, freight forwarders and authorities. These systems are critical infrastructures – successful cyber attacks can lead to significant transport disturbances and severe consequences for the whole economy. This paper presents ongoing work within the research project PortSec, aiming at improved resilience of PCSs with respect to cyber attacks.