The most effective control for protecting the confidentiality and integrity of data stored unencrypted on virtual machines is to monitor access to stored images and snapshots of virtual machines. Images and snapshots are copies of virtual machines that can be used for backup, restoration, or cloning purposes. If data stored on virtual machines are unencrypted, they may be exposed or compromised if unauthorized or malicious users access or copy the images or snapshots. Therefore, monitoring access to stored images and snapshots can help detect and prevent any unauthorized or suspicious activities, and provide audit trails for accountability and investigation.
Restricting access to images and snapshots of virtual machines, limiting creation of virtual machine images and snapshots, and reviewing logical access controls on virtual machines regularly are not the most effective controls for protecting the confidentiality and integrity of data stored unencrypted on virtual machines. These controls may help reduce the risk or impact of data exposure or compromise, but they do not provide sufficient visibility or assurance of data protection. Restricting access to images and snapshots may not prevent authorized users from abusing their privileges or credentials. Limiting creation of virtual machine images and snapshots may not address the existing copies that may contain sensitive data. Reviewing logical access controls on virtual machines regularly may not reflect the actual access activities on images and snapshots.

The IS quality assurance (QA) group is responsible for ensuring that program changes adhere to established standards. Program changes are modifications made to software applications or systems to fix errors, improve performance, add functionality, or meet changing requirements. Program changes should follow established standards for documentation, authorization, testing, implementation, and review. The IS QA group is responsible for verifying that program changes comply with these standards and meet the expected quality criteria. Designing procedures to protect data against accidental disclosure; ensuring that the output received from system processing is complete; and monitoring the execution of computer processing tasks are not responsibilities of the IS QA group. References: [ISACA CISA Review Manual 27th Edition], page 304.

User requirements are statements that describe what the users expect from the software system in terms of functionality, quality, and usability. They are essential inputs for the software development process, as they guide the design, implementation, testing, and deployment of the system. Therefore, an IS auditor's greatest concern when reviewing the early stages of a software development project would be the lack of acceptance criteria behind user requirements. Acceptance criteria are measurable conditions that define when a user requirement is met or satisfied. They help ensure that the user requirements are clear, complete, consistent, testable, and verifiable. Without acceptance criteria, it would be difficult to evaluate whether the system meets the user expectations and delivers value to the organization. Technical documentation, such as program code, is usually produced in later stages of the software development process. Completion of all requirements at the end of each sprint is not mandatory in agile software development methods, as long as there is a prioritized backlog of requirements that can be delivered incrementally. A detailed unit and system test plan is also important for ensuring software quality, but it depends on well-defined user requirements and acceptance criteria. References: Information Systems Acquisition, Development & Implementation, CISA Review Manual (Digital Version)

A demilitarized zone (DMZ) is a network segment that is separated from the internal network and the external network, such as the internet, by firewalls or other security devices. A DMZ provides an extra layer of security for the organization's internal network by isolating the servers and services that need to be accessible to external users, such as a file server, from the rest of the network. A DMZ also prevents external users from accessing the internal network directly, as they have to go through two firewalls to reach it. Therefore, setting up a DMZ is an IS auditor's best recommendation to protect an organization from attacks when its file server needs to be accessible to external users12.
The other possible options are:
* Enforce a secure tunnel connection: This means that the organization requires external users to establish a secure and encrypted connection, such as a virtual private network (VPN), to access its file server.
This can provide some level of security and privacy for the data transmission, but it does not protect the file server or the internal network from attacks if the connection is compromised or if the external users are malicious. Therefore, enforcing a secure tunnel connection is not an IS auditor's best recommendation to protect an organization from attacks when its file server needs to be accessible to external users3.
* Enhance internal firewalls: This means that the organization improves the security and performance of its internal firewalls, which are devices that filter and control the network traffic between different segments of the network. This can provide some level of protection for the internal network from unauthorized or malicious access, but it does not protect the file server or the external network from attacks if the file server is exposed to the internet or if the external network is compromised. Therefore, enhancing internal firewalls is not an IS auditor's best recommendation to protect an organization from attacks when its file server needs to be accessible to external users4.
* Implement a secure protocol: This means that the organization uses a secure and standardized protocol, such as Secure File Transfer Protocol (SFTP) or Secure Shell (SSH), to transfer files between its file server and external users. This can provide some level of security and integrity for the data transmission, but it does not protect the file server or the internal network from attacks if the protocol is exploited or if the external users are malicious. Therefore, implementing a secure protocol is not an IS auditor's best recommendation to protect an organization from attacks when its file server needs to be accessible to external users5. References: 1: What Is a DMZ Network and Why Would You Use It? | Fortinet 2: Demilitarised zone (DMZ) | Cyber.gov.au 3: What Is VPN Tunneling? | Fortinet 4: Firewall
- Wikipedia 5: Secure Shell - Wikipedia