Substantive testing © provides the best evidence of the validity and integrity of logs in an organization’s security information and event management (SIEM) system, because it is a type of audit testing that directly examines the accuracy, completeness, and reliability of the data and transactions recorded in the logs. Substantive testing can involve various methods, such as re-performance, inspection, observation, inquiry, or computer-assisted audit techniques (CAATs), to verify the existence, occurrence, valuation, ownership, presentation, and disclosure of the log data1. Substantive testing canalso detect any errors, omissions, alterations, or manipulations of the log data that may indicate fraud or misstatement2.

Compliance testing (A) is not the best evidence of the validity and integrity of logs in an organization’s SIEM system, because it is a type of audit testing that evaluates the design and effectiveness of the internal controls that are implemented to ensure compliance with laws, regulations, policies, and procedures. Compliance testing can involve various methods, such as walkthroughs, questionnaires, checklists, or flowcharts, to assess the adequacy, consistency, and operation of the internal controls1. Compliance testing can provide assurance that the log data are generated and processed in accordance with the established rules and standards, but it does not directly verify the accuracy and reliability of the log data itself2.

Stop-or-go sampling (B) is not a type of audit testing, but a type of sampling technique that auditors use to select a sample from a population for testing. Stop-or-go sampling is a sequential sampling technique that allows auditors to stop testing before reaching the predetermined sample size if the results are satisfactory or conclusive. Stop-or-go sampling can reduce the audit cost and time by avoiding unnecessary testing, but it can also increase the sampling risk and uncertainty by relying on a smaller sample3. Stop-or-go sampling does not provide any evidence of the validity and integrity of logs in an organization’s SIEM system by itself; it depends on the type and quality of the audit tests performed on the selected sample.

Variable sampling (D) is not a type of audit testing, but a type of sampling technique that auditors use to estimate a numerical characteristic of a population for testing. Variable sampling is a statistical sampling technique that allows auditors to measure the amount or rate of error or deviation in a population by using quantitative methods. Variable sampling can provide precise and objective results by using mathematical formulas and confidence intervals4. Variable sampling does not provide any evidence of the validity and integrity of logs in an organization’s SIEM system by itself; it depends on the type and quality of the audit tests performed on the selected sample.