Due professional care was applied by the internal auditor. According to IIA guidance, due professional care involves applying reasonable judgment in all audit circumstances. The auditor's decision to extend the scope of testing based on a fraud risk assessment, even though no issues were initially found, represents a judicious use of professional judgment given the potential risk of fraud. The fact that fraud was later discovered does not necessarily imply a lack of professional care, as audits cannot guarantee the detection of all frauds.References:
IIA Standard 1220 - Due Professional Care