The most appropriate control to prevent unauthorized retrieval of confidential information stored in a business application system is to enforce an internal data access policy. A data access policy defines who can access what data, under what conditions and for what purposes. It also specifies the roles and responsibilities of data owners, custodians and users, as well as the security measures and controls to protect data confidentiality, integrity and availability. By enforcing a data access policy, the organization can ensure that only authorized personnel can retrieve confidential information from the business application system. Applying single sign-on for access control, implementing segregation of duties and enforcing the use of digital signatures are also useful controls, but they are not sufficient to prevent unauthorized data retrieval without a clear and comprehensive data access policy. References:
* CISA Review Manual, 27th Edition, page 2301
* CISA Review Questions, Answers & Explanations Database - 12 Month Subscription2

The best way to prevent accepting bad data from a third-party service provider is to implement business rules to reject invalid data. Business rules are logical expressions that define the business requirements and constraints for specific data elements. They can be used to validate, transform, or filter incoming data from external sources, ensuring that only high-quality data is accepted into the enterprise data warehouse. Business rules can also help to identify and resolve data quality issues, such as missing values, duplicates, outliers, or inconsistencies.

The IS auditor should be most concerned about the lack of follow-up education for staff members who failed the phishing simulation test. Phishing simulation tests are designed to assess the level of awareness and susceptibility of staff members to phishing attacks, and to provide feedback and training to improve their security behavior. If staff members who failed the test do not receive follow-up education, they will not learn from their mistakes and may continue to fall victim to real phishing attacks, which could compromise the security of the organization.
The other options are less concerning for the IS auditor:
* Test results were not communicated to staff members. This is not ideal, as staff members should receive feedback on their performance and learn from the test results. However, this does not necessarily mean that they did not receive any training or education on how to avoid phishing attacks.
* Staff members were not notified about the test beforehand. This is a common practice for phishing simulation tests, as it mimics the real-world scenario where staff members do not know when they will receive a phishing email. The purpose of the test is to measure their spontaneous reaction and awareness, not their preparedness or compliance.
* Security awareness training was not provided prior to the test. This is not a major concern, as the test can serve as a baseline measurement of the current level of awareness and susceptibility of staff members, and as a starting point for providing tailored training and education based on the test results.