One view of intrusion detection systems is that they should be of value to an analyst trying to disprove that an intrusion has taken place. Insurance companies and lawyers, for example, would find such evidence invaluable in assessing liability. Consider the following scenario. A system has both classified and unclassified documents in it. Someone is accused of using a word processing program to save an unclassified copy of a classified document. Discuss if, and how, each of the three forms of intrusion detection mechanisms could be used to disprove this accusation.