Ensuring segregation of duties are implemented within key systems or processes is the best strategy employed by risk management to prevent internal fraud, because it reduces the opportunity for a single person to manipulate or misuse the system or process for fraudulent purposes. Segregation of duties is a control that assigns different roles and responsibilities to different individuals, such that no one person can perform all the steps of a transaction or process. Requiring control owners to conduct an annual control certification, conducting regular internal and external audits on the systems supporting financial reporting, and requiring the information security officer to review unresolved incidents are all useful strategies to detect or deter internal fraud, but they are not the best strategy to prevent it, as they do not directly address the root cause of fraud.
References = Risk and Information Systems Control Study Manual, Chapter 5, Section 5.3.1, page 197