Software that can detect when an unauthorized access has been made to a network. There are a number of types of intrusion detection software. The first is based on the processing of log files; software in this category examine these files looking for unusual activity on a network, for example a repeated attempt to log-in to the network at an unusual time. This type of software only detects intrusion after it has occurred. The second type of software attempts to detect intrusion in real time by monitoring traffic in the network looking for unusual packets of data.