The most reliable evidence is evidence obtained directly by the auditor through independent performance of procedures. ISACA guidance notes that higher-assurance audit work is achieved when evidence is produced directly by auditors, or at least strictly under their control, rather than being supplied by the entity being audited.
Option D is correct because independently performing manual procedures gives the auditor direct control over the evidence-gathering process and reduces reliance on the auditee or control owner. In audit theory and in ISACA-aligned practice, evidence obtained directly by the auditor is generally more reliable than evidence merely provided by the auditee.
Option A is strong evidence because it comes from an independent third party, but it is still inspected rather than generated directly by the auditor. It is generally very reliable, but not as strong as auditor-generated evidence through independent reperformance.
Option B is less reliable because system-generated evidence provided by a control owner still depends on the completeness and integrity of what was selected and presented by the auditee.
Option C is the least reliable among the plausible choices because critical data received from an auditee is subject to the greatest dependence on management representation and auditee-controlled extraction.
Therefore, D is the best answer because evidence generated through procedures performed independently by the auditor is the most reliable.
References (Official ISACA):
ISACA Journal, Capability Maturity Model and Risk Register Integration — “evidence is produced directly by the auditors or, if strictly under the auditors’ control, by the entity’s staff.”
ISACA Journal, A Factory Model Approach to Technology Control Testing — emphasizes gathering evidence, analyzing it, and substantiating results within a governed testing process.
ISACA, ITAF update announcement — confirms ITAF as ISACA’s professional framework for audit standards and guidance.
