The best control to help reduce the risk of fraudulent internal transactions in several business applications is the segregation of duties. Segregation of duties is the principle of dividing the roles and responsibilities of different individuals or groups involved in a business process or an IT service, so that no one person or group has complete control over the entire process or service. Segregation of duties can help to prevent or detect fraud, errors, conflicts of interest, or misuse of resources, by ensuring that there are checks and balances, and that there is adequate oversight and accountability. Segregation of duties can also help to reduce the risk of collusion, compromise, or coercion among the internal staff, by limiting their access and authority to thebusiness applications and data. Periodic user privileges review, log monitoring, and periodic internal audits are also useful controls, but they are not as effective as segregation of duties, as they are reactive and detective measures, rather than proactive and preventive measures. References = CRISC Review Manual, 6th Edition, ISACA, 2015, page 217.