Process Control Systems (PCSs) are the operating core of Critical Infrastructures (CIs). As such, anomaly detection has been an active research field to ensure CI normal operation. Previous approaches have leveraged network level data for anomaly detection, or have disregarded the existence of process disturbances, thus opening the possibility of mislabelling disturbances as attacks and vice versa. In this paper we present an anomaly detection and diagnostic system based on Multivariate Statistical Process Control (MSPC), that aims to distinguish between attacks and disturbances. For this end, we expand traditional MSPC to monitor process level and controller level data. We evaluate our approach using the Tennessee-Eastman process. Results show that our approach can be used to distinguish disturbances from intrusions to a certain extent and we conclude that the proposed approach can be extended with other sources of data for improving results.
Modern Process Control Systems (PCS) exhibit an increasing trend towards the pervasive adoption of commodity, off-the-shelf Information and Communication Technologies (ICT). This has brought significant economical and operational benefits, but it also shifted the architecture of PCS from a completely isolated environment to an open, “system of systems” integration with traditional ICT systems, susceptible to traditional computer attacks. In this paper we present a novel approach to detect cyber attacks targeting measurements sent to control hardware, i.e., typically to Programmable Logical Controllers (PLC). The approach builds on the Gaussian mixture model to cluster sensor measurement values and a cluster assessment technique known as silhouette. We experimentally demonstrate that in this particular problem the Gaussian mixture clustering outperforms the k-means clustering algorithm. The effectiveness of the proposed technique is tested in a scenario involving the simulated Tennessee-Eastman chemical process and three different cyber attacks.