The best answer is D. Lock the employee ' s account to prevent further unauthorized access.
If credentials have been exposed in a phishing incident, the most urgent priority is to contain the threat by preventing attackers from using those credentials. Locking or disabling the affected account is an immediate response step that reduces the risk of unauthorized access, lateral movement, privilege abuse, or data theft.
Why the other options are incorrect:
A). Notify all employees about the phishing attack and instruct them to avoid suspicious emails.Awareness messaging may be useful later, but it does not immediately contain the compromised account.
B). Wait for confirmation from the employee before making any changes to the account.Waiting introduces unnecessary risk if the credentials are already exposed.
C). Reimage the employee ' s workstation to ensure no malware is present.Reimaging may be appropriate if malware was delivered, but the question specifically says the employee exposed credentials. The first priority is account containment.
From a Security+ incident response perspective, the immediate action after credential compromise is to disable or lock the account, making D the best answer.

A bastion host is a special-purpose server that is designed to withstand attacks and provide secure access to internal resources. A bastion host is usually placed on the edge of a network, acting as a gateway or proxy to the internal network. A bastion host can be configured to allow only certain types of traffic, such as SSH or HTTP, and block all other traffic. A bastion host can also run security software such as firewalls, intrusion detection systems, and antivirus programs to monitor and filter incoming and outgoing traffic. A bastion host can provide administrative access to internal resources by requiring strong authentication and encryption, and by logging all activities for auditing purposes12.
A bastion host is the most secure method among the given options because it minimizes the traffic allowed through the security boundary and provides a single point of control and defense. A bastion host can also isolate the internal network from direct exposure to the internet or other untrusted networks, reducing the attack surface and the risk of compromise3.
Deploying a perimeter network is not the correct answer, because a perimeter network is a network segment that separates the internal network from the external network. A perimeter network usually hosts public- facing services such as web servers, email servers, or DNS servers that need to be accessible from the internet. A perimeter network does not provide administrative access to internal resources, but rather protects them from unauthorized access. A perimeter network can also increase the complexity and cost of network management and security4.
Installing a WAF is not the correct answer, because a WAF is a security tool that protects web applications from common web-based attacks by monitoring, filtering, and blocking HTTP traffic. A WAF can prevent attacks such as cross-site scripting, SQL injection, or file inclusion, among others. A WAF does not provide administrative access to internal resources, but rather protects them from web application vulnerabilities. A WAF is also not a comprehensive solution for network security, as it only operates at the application layer and does not protect against other types of attacks or threats5.
Utilizing single sign-on is not the correct answer, because single sign-on is a method of authentication that allows users to access multiple sites, services, or applications with one username and password. Single sign- on can simplify the sign-in process for users and reduce the number of passwords they have to remember and manage. Single sign-on does not provide administrative access to internal resources, but rather enables access to various resources that the user is authorized to use. Single sign-on can also introduce security risks if the user's credentials are compromised or if the single sign-on provider is breached6. References = 1: Bastion host - Wikipedia, 2: 14 Best Practices to Secure SSH Bastion Host - goteleport.com, 3: The Importance Of Bastion Hosts In Network Security, 4: What is the network perimeter? | Cloudflare, 5: What is a WAF? | Web Application Firewall explained, 6: [What is single sign-on (SSO)? - Definition from WhatIs.com]

Detective controls are security measures that are designed to identify and monitor any malicious activity or anomalies on a system or network. They can help to discover the source, scope, and impact of an attack, and provide evidence for further analysis or investigation. Detective controls include log files, security audits, intrusion detection systems, network monitoring tools, andantivirus software. In this case, the administrator used log files as a detective control to review the ransomware attack on the company's system. Log files are records of events and activities that occur on a system or network, such as user actions, system errors, network traffic, and security alerts. They can provide valuable information for troubleshooting, auditing, and forensics.
References:
Security+ (Plus) Certification | CompTIA IT Certifications, under "About the exam", bullet point 3: "Operate with an awareness of applicable regulations and policies, including principles of governance, risk, and compliance." CompTIA Security+ Certification Kit: Exam SY0-701, 7th Edition, Chapter 1, page 14: "Detective controls are designed to identify and monitor any malicious activity or anomalies on a system or network." Control Types - CompTIA Security+ SY0-401: 2.1 - Professor Messer IT ..., under "Detective Controls":
"Detective controls are security measures that are designed to identify and monitor any malicious activity or anomalies on a system or network."

FIM stands for File Integrity Monitoring, which is a method to secure data by detecting any changes or modifications to files, directories, or registry keys. FIM can help a security administrator track any unauthorized or malicious changes to the data, as well as verify the integrity and compliance of the data. FIM can also alert the administrator of any potential breaches or incidents involving the data.
Some of the benefits of FIM are:
It can prevent data tampering and corruption by verifying the checksums or hashes of the files.
It can identify the source and time of the changes by logging the user and system actions.
It can enforce security policies and standards by comparing the current state of the data with the baseline or expected state.
It can support forensic analysis and incident response by providing evidence and audit trails of the changes.
References:
CompTIA Security+ SY0-701 Certification Study Guide, Chapter 5: Technologies and Tools, Section 5.3:
Security Tools, p. 209-210
CompTIA Security+ SY0-701 Certification Exam Objectives, Domain 2: Technologies and Tools, Objective
2.4: Given a scenario, analyze and interpret output from security technologies, Sub-objective: File integrity monitor, p. 12