Which of the following would best prevent unauthorized external changes to an organization ' s...

Unauthorized external changes to data are best prevented through layered preventive controls. A firewall restricts unauthorized network access from external sources. Antivirus software helps prevent malicious code from modifying or corrupting data. Data encryption protects data confidentiality and can reduce unauthorized use or alteration when combined with proper key controls. Backup procedures are important recovery controls, but they do not prevent unauthorized changes from occurring. Change logs are detective controls because they record activity after changes occur. Internal auditors evaluating data protection should distinguish preventive, detective, and corrective controls. The best preventive combination listed is antivirus software, firewall, and encryption. Therefore, Option A is correct.