The IS auditor's most important course of action after finding that several similar incidents were logged during the audit period is to determine if a root cause analysis was conducted. A root cause analysis is a systematic process that identifies the underlying causes of system failures or incidents. A root cause analysis can help to prevent recurrence of similar incidents, improve system performance and reliability, and enhance incident management processes. The IS auditor should evaluate whether a root cause analysis was performed for each incident, whether it was timely and thorough, and whether it resulted in effective corrective actions.