To bring custom objects with sensitive data to protected status in the AppExchange Security Review, follow these best practices:
1. **Use Protected Custom Metadata or Settings**: Store sensitive data like API keys or passwords in protected custom metadata fields or settings for secure management.
2. **Encrypt Sensitive Data**: If sensitive data is stored in custom objects, encrypt it using the Apex Crypto API and store the encryption key separately in protected custom settings or metadata.
3. **Set Permissions Carefully**: Configure field permissions to ensure only authorized users or processes can access sensitive data.
4. **Avoid Public Visibility**: Do not use public custom settings, objects, or metadata for sensitive data to prevent unauthorized access.
5. **Secure Coding Practices**: Prevent vulnerabilities like SOQL injection and unauthorized access by sanitizing inputs and enforcing CRUD/FLS checks.
6. **Leverage Named Credentials**: Use named credentials for locally generated or per-org secrets, but note that administrators can view these.
7. **Thorough Reviews and Testing**: Use tools like the Salesforce Security Scanner and conduct manual reviews to identify vulnerabilities. Document false positives with evidence for the review process.
8. **Follow Salesforce Guidelines**: Adhere to AppExchange Security Review policies and Salesforce's standards for secure data handling.
By following these steps, you can enhance security and meet the AppExchange Security Review requirements.