This document summarizes a research paper that proposes using principal component analysis (PCA) as a dimension reduction technique for intrusion detection systems (IDS). The paper applies PCA to reduce the number of features from 41 to either 6 or 10 features for the NSL-KDD dataset. One reduced feature set is used to develop a network IDS with high detection success and rate, while the other is used for a host IDS also with good detection success and very high detection rate. The paper outlines the process of applying PCA for IDS, including performing PCA on training data to identify principal components, then using those components to map new online data and detect intrusions based on deviation thresholds.