Cybersecurity ISA-IEC-62443 Exam Questions and Answers PDF

ISA/IEC 62443 defines Security Levels (SL 0–4) as qualitative representations of the system’s ability to withstand different attacker capabilities. These definitions are consistent across system (3-3) and component (4-2) requirements.

Step 1: Understanding attacker models

SL 1 addresses casual or accidental misuse.

SL 2 addresses intentional violations using simple means and low skill.

SL 3 addresses intentional violations using sophisticated means with moderate skills.

SL 4 addresses highly sophisticated attackers with extended resources.

Step 2: Match requirement to definition

The question explicitly describes:

Intentional violations

Sophisticated means

Moderate skill level

This description directly aligns with the formal definition of SL 3.

Step 3: Why other SLs do not fit

SL 1 and SL 2 do not account for sophisticated attack techniques.

SL 4 assumes nation-state–level capability and extensive resources, which exceeds the stated threat.

Step 4: Risk-based targeting

ISA/IEC 62443-3-2 requires asset owners to select a Target Security Level (SL-T) based on risk assessment. When threats involve deliberate, technically capable attackers but not extreme resources, SL 3 is the appropriate target.

Therefore, the correct and standards-aligned answer is SL 3.

Modbus TCP is a widely used protocol in industrial control systems, enabling communication between devices such as PLCs and SCADA systems over Ethernet networks. It is an adaptation of the classic Modbus protocol to TCP/IP networks and is explicitly referenced in ISA/IEC 62443 documentation as a common protocol for IACS communications. FTP, HTTP, and SMTP are general IT protocols and not primarily associated with industrial control communications.

 Intrusion detection systems (IDS) are tools that monitor network traffic and detect suspicious or malicious activity based on predefined rules or signatures. They are effective against known vulnerabilities, as they can alert the system administrators or security personnel when they encounter a match with a known attack pattern or behavior. However, IDS have some limitations and challenges, especially when applied to industrial automation and control systems (IACS). Some of these are:

Modern IDS do not recognize IACS devices by default, as they are designed for general-purpose IT networks and protocols. Therefore, they may generate false positives or negatives when dealing with IACS-specific devices, protocols, or traffic patterns. To overcome this, IDS need to be customized or adapted to the IACS environment and context, which may require additional expertise and resources.

They are not very inexpensive to design and deploy, as they require careful planning, configuration, testing, and maintenance. They also need to be integrated with other security tools and processes, such as firewalls, antivirus, patch management, incident response, etc. Moreover, they may introduce additional costs and risks, such as network performance degradation, data privacy issues, or legal liabilities.

They are not effective against unknown or zero-day vulnerabilities, as they rely on predefined rules or signatures that may not cover all possible attack scenarios or techniques. Therefore, they may fail to detect novel or sophisticated attacks that exploit new or undiscovered vulnerabilities. To mitigate this, IDS need to be complemented with other security measures, such as anomaly detection, threat intelligence, or machine learning.

They require a significant amount of care and feeding, as they need to be constantly updated, tuned, and monitored. They also generate a large amount of data and alerts, which may overwhelm the system administrators or security personnel. Therefore, they need to be supported by adequate tools and processes, such as data analysis, alert filtering, prioritization, correlation, or visualization.

Packet filter, application proxy, and stateful inspection are all recognized types or classes of firewalls in both IT and industrial control environments. A network monitor, on the other hand, is not considered a firewall but rather a tool for observing and analyzing network traffic. It does not provide firewall-like controls for blocking or allowing traffic.