Not all hackers engage in criminal activity, making option B the correct answer. The term "hacker" broadly refers to individuals with technical skills to understand and manipulate systems. Their intent determines whether their actions are ethical or malicious.
Ethical hackers, also known as White Hat hackers, work legally and with authorization to identify vulnerabilities in systems, networks, and applications. When they discover security weaknesses, they follow responsible disclosure practices by reporting findings to the affected organization so issues can be fixed promptly.
Option A is incorrect because it incorrectly generalizes all hackers as criminals. Option C is incorrect because selling stolen information describes malicious actors, often referred to as Black Hat hackers.
Understanding this distinction is important when analyzingcurrent security trends, as ethical hacking has become a legitimate profession. Many organizations now rely on penetration testers, bug bounty programs, and internal security teams to proactively defend against cyber threats.
Ethical hacking contributes to safer digital environments by helping organizations strengthen defenses before attackers exploit vulnerabilities. Recognizing that hacking skills can be used constructively supports responsible security practices and professional cybersecurity development.

A firewall is a fundamental information security control designed to monitor, filter, and control incoming and outgoing network traffic based on predefined security rules. This makes option A the correct answer.
Firewalls act as a barrier between trusted internal networks and untrusted external networks, such as the internet. They can be implemented as hardware devices, software applications, or cloud-based services.
Ethical hackers must understand firewall behavior because it directly affects reconnaissance, exploitation techniques, and attack surface visibility.
Option B is incorrect because antivirus software focuses on malware detection, not traffic filtering. Option C is incorrect because a firewall is a defensive security mechanism, not an attack method.
From an ethical hacking perspective, firewalls are evaluated during security assessments to identify misconfigurations, overly permissive rules, or exposed services. Poorly configured firewalls may allow unauthorized access, while overly restrictive ones may disrupt legitimate business operations.
Firewalls play a critical role in enforcing network segmentation, access control, and defense-in-depth strategies. When combined with intrusion detection systems, endpoint security, and proper monitoring, they significantly reduce the risk of unauthorized access.
Understanding firewall concepts enables ethical hackers and defenders to design stronger network architectures and respond effectively to modern cyber threats.

Cross-Site Scripting (XSS) is aweb application security vulnerabilitythat allows attackers to inject malicious client-side scripts into trusted web pages. This makes option A the correct answer. XSS occurs when applications fail to properly validate, sanitize, or encode user input before displaying it to other users.
When an XSS vulnerability is exploited, the injected script runs in the victim's browser within the security context of the vulnerable website. This can lead to session hijacking, cookie theft, credential harvesting, keylogging, or redirection to malicious websites. XSS is commonly categorized intostored XSS, reflected XSS, and DOM-based XSS, all of which ethical hackers test during web application assessments.
Option B is incorrect because cloned websites are typically associated with phishing attacks, not XSS vulnerabilities. Option C is incorrect because XSS is primarily a web-based vulnerability, not a mobile- specific issue involving balance or contact theft.
From a defensive perspective, understanding XSS is critical for implementing secure coding practices such as input validation, output encoding, Content Security Policy (CSP), and proper use of modern frameworks.
Ethical hackers test for XSS to help organizations prevent client-side attacks and protect user data.

A reverse shell is a fundamental technique used during the exploitation phase of a penetration test to gain interactive access to a target system. In a standard shell connection (Bind Shell), the attacker initiates a connection to a specific port on the victim's machine. However, modern network security controls, such as firewalls and Network Address Translation (NAT), almost always block unsolicited inbound connections. To bypass these restrictions, ethical hackers utilize a "reverse shell." In this scenario, the attacker first sets up a listener on their own machine (using a tool like Netcat or Metasploit) on a common outbound port, such as 80 (HTTP) or 443 (HTTPS). The attacker then executes a payload on the victim's machine that instructs it to initiate an outbound connection back to the attacker's listener.
Since most firewalls are configured to be permissive with outbound traffic (to allow users to browse the web), the connection from the victim to the attacker is often successful. Once the connection is established, the victim's machine hands over control of its command-line interface to the attacker. This allows the attacker to execute commands as if they were sitting at the victim's keyboard. The power of a reverse shell lies in its ability to circumvent perimeter defenses and provide a stable platform for post-exploitation activities, such as privilege escalation or lateral movement. From a defensive standpoint, organizations can mitigate this threat by implementing strict egress (outbound) filtering, which limits the ports and IP addresses that internal servers can communicate with. Monitoring for unusual outbound traffic patterns and using EDR (Endpoint Detection and Response) tools to identify unauthorized shell processes are also critical components of a robust security strategy designed to detect and terminate active reverse shell connections.

Active reconnaissance is a phase of ethical hacking in which information is gathered bydirectly interacting with the target system. This makes option C the correct answer. Unlike passive reconnaissance, active reconnaissance involves sending requests, probes, or packets to the target to elicit responses that reveal useful technical details.
Common active reconnaissance techniques includeport scanning,service enumeration,banner grabbing,DNS queries, andnetwork mapping. These methods help ethical hackers identify open ports, running services, operating systems, and potential vulnerabilities. Active reconnaissance is typically conducted after passive techniques have provided initial intelligence.
Option A is incorrect because recognizing a target without action does not describe reconnaissance behavior.
Option B is also incorrect because observing without interaction definespassive reconnaissance, not active reconnaissance.
From an ethical hacking perspective, active reconnaissance is more intrusive and therefore more likely to be detected by intrusion detection systems or firewalls. Because of this, it must always be performed withexplicit authorization. Despite the increased risk of detection, active reconnaissance provides far more accurate and actionable information, making it essential for effective penetration testing.
Understanding the distinction between active and passive reconnaissance helps security professionals choose the correct techniques based on scope, authorization, and risk tolerance. Properly managed, active reconnaissance enables organizations to identify weaknesses early and strengthen their defensive security posture.