A method of detecting intrusions on a computer includes the step of identifying an internet protocol field range describing fields within internet protocol packets received by a computer. A connectivity range is also established which describes a distribution of network traffic received by the computer. An internet protocol field threshold and a connectivity threshold are then determined from the internet protocol field range and connectivity range, respectively. During the operation of the computer, values are calculated for the internet protocol field range and connectivity range. These values are compared to the internet protocol metric threshold and connectivity metric threshold so as to identify an intrusion on the computer.