1. A computer implemented method of monitoring the operational state of a computer, the method comprising: running, on the monitored computer, a monitoring program to monitor a set of activity parameters indicative of the activity of the monitored computer; providing the monitored activity parameters to a monitoring system; and running, on the monitoring system, a comparison program which: i) compares the set of activity parameters provided by the monitored computer with a model which defines a predetermined operational state of the monitored computer in which the monitored computer is not fulfilling an allocated role, and ii) produces an indication of whether or not the monitored computer complies with the model.