The finding that should be of greatest concern to an IS auditor reviewing data conversion and migration during the implementation of a new application system is that unauthorized data modifications occurred during conversion. Data conversion and migration is a process that involves transferring data from one system to another, ensuring its accuracy, completeness, integrity, and usability. Unauthorized data modifications during conversion can result in data loss, corruption, inconsistency, or duplication, which can affect the functionality, performance, reliability, and security of the new system. Unauthorized data modifications can also have serious business implications, such as affecting decision making, reporting, compliance, customer service, and revenue. The IS auditor should verify that adequate controls are in place to prevent, detect, and correct unauthorized data modifications during conversion, such as access control, data validation, reconciliation, audit trail, and backup and recovery. The other findings (A, B and D) are less concerning, as they can be mitigated by documenting the change management process, restoring the backups of the old system and data from offline storage, or automating the data conversion process. References: CISA Review Manual (Digital Version), Chapter 3: Information Systems Acquisition, Development & Implementation, Section 3.4: System Implementation

The best recommendation to prevent fraudulent electronic funds transfers by accounts payable employees is dual control. Dual control is a segregation of duties control that requires two or more individuals to perform or authorize a transaction or activity. Dual control can prevent fraudulent electronic funds transfers by requiring independent verification and approval of payment requests, amounts, and recipients by different accounts payable employees. The other options are not as effective as dual control in preventing fraudulent electronic funds transfers, as they do not involve independent checks or approvals. Periodic vendor reviews are detective controls that can help identify any irregularities or anomalies in vendor payments, but they do not prevent fraudulent electronic funds transfers from occurring. Independent reconciliation is a detective control that can help compare and confirm payment records with bank statements, but it does not prevent fraudulent electronic funds transfers from occurring. Re-keying of monetary amounts is an input control that can help detect any errors or discrepancies in payment amounts, but it does not prevent fraudulent electronic funds transfers from occurring. References: CISA Review Manual (Digital Version), Chapter 3, Section 3.2