Most people say that collusion can not be prevented by the system. Opinion was some truth, say in the field of information technology, those who master the technology certainly holds the key or simply mess up the existing system. But it is a choice, preparation of control systems must also consider the cost and benefit.
Any systems of control can defeated if a sufficient number of dishonest key individual conspire to subvert them and are able to falsify the relevant documents. A sufficiently complex set of controls can make it difficult to assemble the needed number of conspirators, but potentially great cost in organizational inefficiency.
Conspiracies of this sort usually come to the light when they are observed (and reported) by someone who is not a party to the conspiracy, or when there is a falling out among the conspirators. They may also be detected during routine audit if substantial amounts of funds are involved or if the conspirators are not sufficiently careful in falsifying the documents.
