Ace the CISA Domain 1 Exam 2026 – Your Gateway to Cyber Success!

The choice of the results of a test performed by an external IS auditor is considered the most reliable form of evidence because it provides an independent and objective evaluation of the processes or controls being audited. External auditors bring a level of objectivity that internal auditors may not possess due to potential biases associated with familiarity with the organization or its personnel.

When an external IS auditor performs tests, their findings are based on established auditing standards and methodologies, which enhances the credibility of the evidence collected. Their professional judgment is also informed by years of experience and knowledge of industry standards, making the conclusions drawn from their tests highly regarded.

This reliability is further bolstered by the fact that external auditors are obligated to adhere to strict ethical guidelines, ensuring that their assessment is impartial. In contrast, evidence gathered from oral statements or internal reports lacks this independent verification, making them less reliable in the context of an audit.

Confirmation letters from outside sources can also be trustworthy, but the testing and conclusions derived from a thorough audit conducted by an external entity often provide a broader scope of assessment, making them a stronger form of evidence overall.