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

A change log is a record of all changes made to a system or application, including the date, time, description, and approval of each change. A change log can help an IS auditor to trace the source and authorization of a modification to a system's security settings. A system event correlation report is a tool that analyzes data from multiple sources to identify patterns and anomalies that indicate potential security incidents. A database log is a record of all transactions and activities performed on a database, such as queries, updates, and backups. A security incident and event management (SIEM) report is a tool that collects, analyzes, and reports on data from various sources to detect and respond to security incidents.

The most useful tool for determining whether the goals of IT are aligned with the organization's goals is a balanced scorecard. A balanced scorecard is a strategic management system that translates an organization's vision and mission into a set of objectives and measures across four perspectives: financial, customer, internal process, and learning and growth. A balanced scorecard helps align IT goals with organizational goals by linking them to a common strategy map that shows how IT contributes to value creation and performance improvement in each perspective. A balanced scorecard also helps monitor and evaluate IT performance against predefined targets and indicators.
Enterprise dashboard, enterprise architecture (EA), and key performance indicators (KPIs) are not the most useful tools for determining whether the goals of IT are aligned with the organization's goals. These tools may help communicate, design, or measure IT goals or activities, but they do not provide a comprehensive framework for aligning IT goals with organizational goals across multiple dimensions.

The best method for maintaining the security of corporate applications pushed to employee-owned mobile devices is implementing mobile device management (MDM). MDM is a software solution that allows an organization to remotely manage, configure, and secure the mobile devices that access its network and data.
MDM can help protect corporate applications on employee-owned devices by:
Enforcing security policies and settings, such as encryption, password, firewall, antivirus, and VPN.
Controlling the installation, update, and removal of corporate applications and data.
Separating corporate and personal data and applications on the device using containers or profiles.
Monitoring and auditing the device's compliance status, activity, and location.
Performing remote actions, such as lock, wipe, backup, or restore, in case of loss, theft, or compromise.
MDM can provide a comprehensive and centralized approach to maintain the security of corporate applications on employee-owned devices, regardless of the device type, platform, or ownership. MDM can also help the organization comply with regulatory and industry standards for data protection and privacy.
Enabling remote data destruction capabilities is a useful feature for maintaining the security of corporate applications on employee-owned devices, but it is not the best method by itself. Remote data destruction allows the organization to erase the corporate data and applications from the device in case of loss, theft, or compromise. However, this feature does not prevent unauthorized access or misuse of the corporate data and applications before they are destroyed. Remote data destruction is usually part of an MDM solution.
Disabling unnecessary network connectivity options is a good practice for maintaining the security of corporate applications on employee-owned devices, but it is not the best method by itself. Network connectivity options, such as Wi-Fi, Bluetooth, NFC, or USB, can expose the device to potential attacks or data leakage. Disabling these options when they are not needed can reduce the attack surface and improve battery life. However, this practice does not address other security risks or requirements for the corporate applications on the device. Disabling network connectivity options can also be part of an MDM solution.
Requiring security awareness training for mobile users is an important measure for maintaining the security of corporate applications on employee-owned devices, but it is not the best method by itself. Security awareness training can educate the users about the potential threats and best practices for using their devices securely. It can also help foster a culture of security and responsibility among the users. However, security awareness training cannot guarantee that the users will follow the security policies and guidelines consistently and correctly. Security awareness training should be complemented by technical controls, such as MDM.
References:
Protecting Corporate Data on Mobile Devices for All Companies1
Mobile Device Security: Corporate-Owned Personally-Enabled (COPE)23