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Introduction:
The convergence of Information Technology (IT) and Operational Technology (OT) has created one of the most significant security blind spots in modern enterprises. Industrial Control Systems (ICS) and Supervisory Control and Data Acquisition (SCADA) environments – the backbone of power grids, water treatment facilities, and manufacturing plants – are increasingly targeted by sophisticated threat actors. Mike Holcomb, a recognized authority in OT/ICS security, has released a comprehensive library of 153 free educational videos covering everything from beginner fundamentals to advanced penetration testing, providing an unprecedented free resource for security professionals transitioning into this high-demand field. This article distills the essential technical knowledge from this extensive video series, offering a structured roadmap, practical commands, and actionable defense strategies for securing critical infrastructure in 2026 and beyond.
Learning Objectives:
- Master the foundational concepts of OT/ICS architecture, including the Purdue Model, PLCs, and the critical differences between IT and OT security priorities
- Execute practical penetration testing techniques against industrial protocols like Modbus using open-source tools
- Implement defensive strategies including network segmentation, secure remote access, and backup/recovery best practices
- Leverage generative AI tools like ChatGPT for both offensive reconnaissance and defensive hardening in ICS environments
You Should Know:
- Your 2026 OT/ICS Security Roadmap – Certifications and Career Pathways
The journey into OT/ICS cybersecurity requires a strategic approach to certification and skill development. According to Holcomb’s 2026 roadmap, professionals transitioning from IT must first master networking fundamentals – attackers enter OT networks through the same TCP/IP stacks that IT professionals already understand. The certification landscape has evolved significantly, with three primary pathways emerging:
- CompTIA SecOT+: A new, cost-effective entry point at approximately $400+, ideal for testing the waters without significant financial investment
- SANS Training Route: Premium certifications including GICSP, GRID, and GCIP for those with larger training budgets
- ISA/IEC 62443 Route: A modular approach allowing professionals to build credentials over time toward the Cybersecurity Expert designation
The strategic recommendation is clear: learn fundamentals through free resources, secure entry-level positions, and let employers fund advanced certifications. This approach mirrors the broader industry trend where hands-on practical skills increasingly outweigh certification alone.
- Hacking PLCs with Modbus – The Swiss Army Knife Approach
Programmable Logic Controllers (PLCs) running unsecure protocols like Modbus represent one of the most accessible attack vectors in OT environments. Attackers can read data stored in memory and make modifications without ever being challenged for credentials – no username, no password required.
The Modbus Swiss Army Knife, an open-source utility available at https://github.com/utilsec/Modbus-Tools, demonstrates just how trivial these attacks can be. Here’s a practical step-by-step guide to understanding the risk:
Step 1: Identify Modbus Devices on the Network
nmap -p 502 --open --script modbus-discover <target_network>/24
This scans for devices with port 502 open (default Modbus TCP) and attempts to enumerate device information.
Step 2: Read Coil States
Using the Modbus tools:
python modbus_read.py -a <device_ip> -r 0 -c 10
This reads the state of 10 coils starting at address 0.
Step 3: Write to a Coil (The Attack)
python modbus_write.py -a <device_ip> -r 0 -v 1
This forces coil 0 to the ON position – potentially starting or stopping physical equipment.
Step 4: Monitor Operational Modes
Security teams should implement continuous monitoring for unexpected mode changes, as PLCs can be switched from “Run” to “Program” mode, allowing unauthorized logic uploads.
The critical takeaway: many organizations still fail to implement basic backup and recovery programs, resulting in extended outages with significant costs. The 1 security control in OT/ICS? Backup and recovery.
- Nmap Scanning in ICS/OT Environments – Discovery Without Disruption
Nmap remains the quintessential network discovery tool, but scanning industrial networks requires extreme caution. Aggressive scans can disrupt deterministic traffic patterns and cause unintended physical consequences. Holcomb’s video on Nmap scanning for ICS/OT networks provides essential guidance for safe reconnaissance.
Safe Scanning Methodology:
Step 1: Passive Discovery First
Before any active scanning, perform passive analysis:
tcpdump -i eth0 -1 -s 0 -w ot_traffic.pcap
Capture traffic for 24-48 hours to understand normal baseline behavior.
Step 2: Low-Intensity Active Scanning
Use conservative timing templates:
nmap -T2 -p 502,44818,2222,80,443 --open <target_ip>
The `-T2` (polite) timing reduces packet rate to minimize disruption.
Step 3: Protocol-Specific Enumeration
For Modbus devices:
nmap -p 502 --script modbus-enum <target_ip>
For EtherNet/IP (CIP) devices:
nmap -p 44818 --script enip-enumerate <target_ip>
Step 4: Asset Register Creation
Build an asset register from captured PCAPs using tools like:
tshark -r ot_traffic.pcap -T fields -e ip.src -e ip.dst -e tcp.srcport -e tcp.dstport | sort | uniq
This provides a baseline inventory of communicating devices.
Critical Warning: Never perform vulnerability scans (Nessus, OpenVAS) or aggressive Nmap scans against production OT networks without explicit authorization and thorough change management.
4. Building Secure IT/OT DMZs and Network Segmentation
The Purdue Model for Industrial Control Systems provides the foundational architecture for secure OT networks, mapping Levels 0 through 5 from physical processes to enterprise IT. Proper implementation requires:
Step 1: Implement the IT/OT DMZ
Create a demilitarized zone between corporate IT networks (Levels 4-5) and industrial control networks (Levels 0-3). This DMZ hosts services like:
– Patch management servers
– Antivirus update servers
– Historian databases
– Remote access gateways
Step 2: Deploy Industrial Firewalls
Configure firewalls with application-layer inspection for industrial protocols:
access-list 101 permit tcp <IT_subnet> <DMZ_subnet> eq 443 access-list 101 permit tcp <OT_subnet> <DMZ_subnet> eq 502 access-list 101 deny ip any any
Step 3: Implement Unidirectional Gateways
For critical environments, consider data diodes that allow one-way data flow from OT to IT, preventing any potential attack vector from reaching control systems.
Step 4: Secure Remote Access
Eliminate weak remote access configurations:
- Require multi-factor authentication (MFA) for all remote connections
- Use jump hosts with session recording
- Implement time-based access controls
- Disable default vendor credentials
Step 5: Vendor Laptop and USB Drive Controls
Vendor maintenance activities represent a significant risk vector. Implement:
– Dedicated vendor access accounts with expiration dates
– Endpoint Detection and Response (EDR) on vendor laptops
– USB port blocking or whitelisting
– Pre-connection health checks
- OSINT for ICS/OT – The 10+ Hour Deep Dive
Open Source Intelligence (OSINT) for industrial control systems involves gathering publicly available information about critical infrastructure without direct interaction. This technique is essential for both attackers (reconnaissance) and defenders (identifying exposed assets).
Step 1: Shodan and Censys Queries
Search for exposed industrial devices:
Shodan: port:502 product:Modbus Shodan: port:44818 "Rockwell Automation" Censys: services.port=502 AND services.banner="Modbus"
Step 2: Google Dorking for ICS Documentation
site:.pdf "PLC" "MODBUS" "configuration" intitle:"index of" "SCADA" "HMI" filetype:pdf "Siemens" "STEP 7" "password"
Step 3: GitHub Repository Analysis
Search for exposed credentials or configuration files:
github.com search: "Modbus" "password" "config" github.com search: "PLC" "credentials" ".cfg"
Step 4: Social Media and Job Postings
Analyze job descriptions for technology stacks, vendor names, and specific system details that reveal infrastructure composition.
Defensive Response: Organizations should conduct regular OSINT assessments of their own exposed assets and implement:
– Network Address Translation (NAT) for all OT devices
– Restrictive firewall rules limiting internet access
– Regular scanning of public IP ranges for OT protocol exposure
- Leveraging ChatGPT for ICS/OT Security – Attack and Defense
Generative AI has become a double-edged sword in cybersecurity. Attackers are already using ChatGPT to develop exploits for ICS environments – defenders must do the same.
Offensive Capabilities (For Testing Only):
Step 1: Python Script Generation
Prompt ChatGPT: “Write a Python script using pymodbus to read all coils from a Modbus device at IP 192.168.1.100”
from pymodbus.client import ModbusTcpClient
client = ModbusTcpClient('192.168.1.100')
client.connect()
result = client.read_coils(0, 10)
print(result.bits)
Step 2: Port Scanner Creation
“Create a basic ICS/OT port scanner that checks for common OT ports (502, 44818, 2222)”
Step 3: PCAP Analysis for Asset Discovery
“Parse this PCAP file and create an asset register of all unique IP addresses and protocols detected”
Defensive Capabilities:
Step 4: Modbus Honeypot Creation
“Write a Python script that creates a Modbus honeypot to log all connection attempts and malicious commands”
Step 5: Security Rule Generation
“Generate Snort rules to detect Modbus function code 15 (write multiple coils) from unauthorized IP addresses”
alert tcp $EXTERNAL_NET any -> $OT_NET 502 (msg:"Modbus Write Multiple Coils"; content:"|0F|"; depth:1; sid:1000001;)
Critical Consideration: Generative AI today is the worst it will ever be – capabilities will only improve. Organizations must build AI literacy into their security teams now.
- The ISA/IEC 62443 Framework – Building Security Programs Step by Step
The ISA/IEC 62443 series provides the global standard for OT/ICS cybersecurity, offering a systematic approach to building security programs. The framework consists of multiple parts addressing:
- General concepts and terminology
- Policies and procedures for IACS security
- System security requirements and security levels
- Component security requirements
- Security for IACS life cycle
Implementation Steps:
Step 1: Conduct a Security Assessment
Map existing controls against ISA/IEC 62443-3-3 (System security requirements):
– Identify zone and conduit boundaries
– Document existing security measures
– Gap analysis against SL1 (Security Level 1) through SL4
Step 2: Develop Security Policies
Create documented procedures for:
- Patch management (with OT-specific testing)
- Incident response (with physical safety considerations)
- Access control (role-based, with MFA)
- Change management (with peer review)
Step 3: Implement Technical Controls
- Firewalls: Industrial-grade with protocol awareness
- Authentication: LDAP/Active Directory integration with MFA
- Monitoring: OT-specific SIEM with protocol parsing
- Backup: Regularly tested, offline backups
Step 4: Continuous Monitoring and Improvement
- Regular vulnerability assessments (in staging environments)
- Security awareness training for OT personnel
- Tabletop exercises simulating realistic attack scenarios
- Regular third-party assessments
What Undercode Say:
- The Skills Gap is Real and Growing: With 153 free videos now available, there is no excuse for security professionals to remain ignorant of OT/ICS security fundamentals. The convergence of IT and OT means that traditional IT security skills are no longer sufficient – understanding industrial protocols, physical safety implications, and the Purdue Model is now table stakes for any serious security practitioner.
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Free Resources Democratize Access: Historically, OT/ICS security training has been prohibitively expensive, with SANS courses costing thousands of dollars. Holcomb’s free video library, combined with open-source tools like the Modbus Swiss Army Knife and Nmap, lowers the barrier to entry significantly. This democratization of knowledge will accelerate the development of the next generation of OT security professionals.
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The Offensive-Defensive Symmetry: Understanding how attackers operate – using tools like ChatGPT to generate exploits, scanning for Modbus devices with Nmap, and leveraging OSINT to identify exposed assets – is essential for building effective defenses. Organizations must adopt a red-team mindset to truly secure their industrial environments.
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Safety First, Always: Unlike traditional IT security where data confidentiality often takes priority, OT security places physical safety and operational integrity above all else. Security controls must be implemented without compromising the deterministic, real-time requirements of industrial processes. This fundamental difference requires a complete paradigm shift in how security is approached.
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The Certification Landscape is Evolving: The introduction of CompTIA SecOT+ alongside established certifications from SANS and ISA/IEC 62443 provides multiple pathways for career development. Professionals should strategically choose certifications based on their career goals, current experience level, and available budget, rather than pursuing credentials arbitrarily.
Prediction:
+1 The proliferation of free OT/ICS security training resources will accelerate the growth of the industrial cybersecurity workforce, potentially reducing the global shortage of qualified professionals by 15-20% over the next three years.
+1 Open-source security tools specifically designed for OT environments (Modbus Swiss Army Knife, GRASSMARLIN, Shodan) will continue to evolve, providing defenders with increasingly sophisticated capabilities that rival commercial offerings.
-1 The increasing accessibility of OT hacking knowledge will inevitably lead to a surge in attacks against critical infrastructure, particularly from ransomware groups who recognize the high-value targets and the willingness of operators to pay large ransums to restore operations.
+1 Regulatory frameworks (NERC CIP, EU NIS2, CISA requirements) will increasingly mandate the type of security controls and training that Holcomb’s videos cover, driving adoption of best practices across the industry.
-1 Organizations that fail to invest in OT security training and basic controls (backup/recovery, network segmentation, MFA) will face increasingly severe consequences, including regulatory fines, operational downtime, and potential physical safety incidents.
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