The auditor's best action is to re-perform the audit before changing the conclusion, because the auditor needs to obtain sufficient and appropriate evidence to support the audit opinion. The evidence provided by IT management may not be reliable or relevant, and it may not reflect the actual effectiveness of the control during the audit period. Therefore, the auditor should verify the evidence independently and test the control again to ensure that it meets the audit criteria and objectives. The other options are not appropriate, because they either ignore or accept the evidence provided by IT management without verification, which may compromise the quality and integrity of the audit. References:
* ISACA, CISA Review Manual, 27th Edition, chapter 1, section 1.51
* ISACA, IT Audit and Assurance Standards, Guidelines and Tools and Techniques for IS Audit and Assurance Professionals, section 12062