1. A computer implemented method of monitoring the operational state of a computer, the method comprising: running on the monitored computer a monitoring program configured 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 predetermined model which defines a predetermined operational state of the monitored computer, and ii) produces an indication of whether or not the monitored computer complies with the model.