This document provides a literature review on automatic intrusion detection systems based on artificial intelligence techniques. It discusses how machine learning algorithms like neural networks, decision trees, KNN, and SVM have been applied to develop intrusion detection systems. Both supervised and unsupervised learning techniques are investigated. The review finds that the NSL-KDD dataset is commonly used and that accuracy, precision, recall, AUC and F1 score are typical evaluation metrics. However, it notes that a limitation of classification-based approaches is the inability to detect novel or modified attack types. The document recommends future work focus on techniques that can identify anomalous intrusions.