Online anomaly detection by using N-gram model and growing hierarchical self-organizing maps

In this research, online detection of anomalous HTTP requests is carried out with Growing Hierarchical Self-Organizing Maps (GHSOMs). By applying an n-gram model to HTTP requests from network logs, feature matrices are formed. GHSOMs are then used to analyze these matrices and detect anomalous requests among new requests received by the webserver. The system proposed is self-adaptive and allows detection of online malicious attacks in the case of continuously updated web-applications. The method is tested with network logs, which include normal and intrusive requests. Almost all anomalous requests from these logs are detected while keeping the false positive rate at a very low level.