The best criteria for monitoring an IT vendor's service levels are the performance metrics, as they provide quantifiable and measurable indicators of how well the vendor is delivering the agreed-upon services, such as availability, reliability, quality, timeliness, and customer satisfaction. A service auditor's report is a document that provides an independent opinion on the vendor's controls and processes, but it may not reflect the actual service levels or performance. A surprise visit to the vendor may help to verify the vendor's compliance and operations, but it may not be feasible or effective for monitoring the service levels on a regular basis. An interview with the vendor may help to obtain feedback and insights from the vendor's perspective, but it may not be objective or reliable for monitoring the service levels. References: CISA Review Manual (Digital Version), Chapter 2: Governance and Management of IT, Section 2.4: IT Service Delivery and Support

The best approach for an IS auditor to evaluate whether the IT strategy supports the organization's vision and mission is to meet with senior management to understand the business goals and how IT can enable them.
This will help the IS auditor to assess the alignment and integration of IT with the business strategy and to identify any gaps or opportunities for improvement. Reviewing ROIs, KPIs, or feedback from other departments may provide some insights, but they are not sufficient to evaluate the IT strategy. References: IS Audit and Assurance Standards, section "Standard 1201: Engagement Planning"

The success of a DLP implementation relies heavily on accurately defining and configuring the policies and rule sets. These configurations ensure that the DLP tool effectively monitors and controls the movement of sensitive data within the organization, thereby preventing data loss.
References
* ISACA CISA Review Manual 27th Edition, Page 301-302 (Data Loss Prevention)

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

Mapping IT processes to roles is an activity that provides an IS auditor with the most insight regarding potential single person dependencies that might exist within the organization. Single person dependencies occur when only one person has the knowledge, skills, or access rights to perform a critical IT function.
Mapping IT processes to roles can help to identify such dependencies and assess their impact on the continuity and security of IT operations. The other activities do not provide as much insight into single person dependencies, as they do not show the relationship between IT processes and roles. References: CISA Review Manual, 27th Edition, page 94