Industrial Control System (ICS) and Operational Technology (OT) security has become a critical priority as nation-state actors and ransomware groups increasingly target critical infrastructure. According to the SANS Institute 2025 Survey, over 22% of organizations reported a cybersecurity incident in the past year, with 40% causing operational disruption. Ransomware attacks targeting OT/ICS environments have surged 87% year-over-year.
This guide covers the fundamentals of securing industrial environments, from basic concepts through building a mature OT security program.
ICS/OT Fundamentals
Key Definitions
Operational Technology (OT): Hardware and software used to monitor, control, and manage industrial processes, infrastructure, and assets across manufacturing, energy, transportation, and utilities.
Industrial Control Systems (ICS): A general term encompassing several types of control systems deployed in critical infrastructure sectors.
ICS Components
| Component | Description | Function |
|---|---|---|
| SCADA | Supervisory Control and Data Acquisition | Collect data and control geographically distributed assets |
| DCS | Distributed Control System | Manage complex processes within localized areas |
| PLC | Programmable Logic Controller | Real-time control of simple, repetitive manufacturing tasks |
| RTU | Remote Terminal Unit | Interface between SCADA master and field devices |
| HMI | Human-Machine Interface | Operator dashboard for monitoring and control |
Industry Sectors
ICS/OT systems are deployed across:
- Electric utilities
- Water and wastewater
- Oil and gas
- Transportation
- Chemical and pharmaceutical
- Food and beverage
- Discrete manufacturing
IT vs OT Security: Critical Differences
Priority Inversion
The most fundamental difference is the inversion of security priorities:
| Priority | IT Security | OT Security |
|---|---|---|
| 1st | Confidentiality | Availability |
| 2nd | Integrity | Integrity |
| 3rd | Availability | Confidentiality |
IT follows CIA (Confidentiality, Integrity, Availability). OT effectively operates under AIC.
Why Availability Dominates OT
- Stopping a production line costs thousands per minute
- Security measures could endanger human lives
- OT systems designed for continuous industrial operations
- Disruptions can cause physical harm or catastrophic failures
Operational Differences
| Aspect | IT | OT |
|---|---|---|
| System lifecycle | 3-5 years | 15-30+ years |
| Downtime tolerance | Scheduled maintenance acceptable | Near-zero tolerance |
| Patching | Regular, automated | Infrequent, manual, complex |
| Security focus | Data protection | Physical process safety |
| Failure impact | Data breach, financial loss | Physical damage, injury, death |
Current State
According to the 2025 State of OT Cybersecurity Report, while over 80% of CISOs now oversee OT, only 35% of organizations have a mature, fully integrated IT/OT security operations model.
The Purdue Model
The Purdue Enterprise Reference Architecture (PERA) is the foundational framework for ICS security, organizing environments into hierarchical zones.
Network Levels
| Level | Name | Components | Purpose |
|---|---|---|---|
| 0 | Physical Process | Sensors, actuators, valves, pumps | Physical components that build products |
| 1 | Basic Control | PLCs, RTUs, IEDs | Direct process control |
| 2 | Supervisory Control | SCADA servers, HMI workstations | Area supervision |
| 3 | Site Operations | Historians, engineering workstations | ICS operations management |
| DMZ | Industrial DMZ | Security controls, data diodes | Buffer between IT and OT |
| 4 | Business Planning | ERP systems, business servers | Business operations |
| 5 | Enterprise | Email, web, external connectivity | Corporate network |
The DMZ
The DMZ between Levels 3 and 4 is critical:
- Creates “air gap” between ICS/OT and IT systems
- Allows data flow with filtering and monitoring
- Enforces security protocols between zones
- Prevents direct connectivity from business to control networks
Security Benefits
Network segmentation per the Purdue Model:
- Provides defense-in-depth strategy
- Limits breach impact through containment
- Prevents lateral movement from business to control networks
- Enables controlled communication through monitored chokepoints
Modern Adaptations
Despite cloud and IIoT challenges, the Purdue Model remains relevant. Modern implementations enhance it with:
- Zero Trust principles
- Microsegmentation within traditional zones
- Software-defined perimeters
- Identity-based access controls
ICS Protocol Vulnerabilities
Modbus
Background: Developed in 1979 for local, trusted environments.
Vulnerabilities:
- No encryption or authentication
- Anyone who can see traffic can read it
- Anyone who can inject packets can send commands
- Direct read/write access to device registers
Attack vectors:
- ARP spoofing for man-in-the-middle attacks
- Command replacement (replacing read with write commands)
- Replay attacks (no session integrity)
DNP3
Background: Commonly used in utilities for SCADA communications.
Vulnerabilities:
- Older implementations lack authentication
- No encryption exposes data to interception
- Bidirectional nature enables abuse of unsolicited responses
- Complexity makes it prone to parsing errors
Mitigation: Secure DNP3 adds authentication and session timeout.
OPC
Vulnerabilities:
- RPC services require appropriate patching
- DCOM uses dynamic ports (1024-65535)
- Difficult to establish solid firewall rules
- OPC DA considered insecure
Secure alternative: OPC UA provides encryption and authentication.
Protocol Security Recommendations
| Practice | Implementation |
|---|---|
| Use secure versions | Secure DNP3, OPC UA |
| Encrypt traffic | TLS tunnels for ICS protocols |
| Filter traffic | Industrial firewalls between zones |
| Network segmentation | Separate IT and OT networks |
ICS-Specific Threats
Major ICS Malware Families
Stuxnet (2010):
- First sophisticated ICS weapon
- Targeted Iranian uranium enrichment centrifuges
- Reprogrammed PLCs to change rotation speeds
- Established that ICS can be weaponized for geopolitical objectives
Industroyer/CrashOverride (2016):
- First malware targeting civilian electrical infrastructure
- Caused blackout in Ukraine
- Leveraged IEC-104 protocol for circuit breaker control
- Attributed to Russia’s Sandworm APT
Triton/TRISIS (2017):
- First malware targeting Safety Instrumented Systems (SIS)
- Targeted Schneider Electric’s Triconex controllers
- Could have risked human lives
- Crossed line by targeting safety systems
Pipedream/INCONTROLLER (2022):
- Most advanced ICS threat discovered
- Targets ubiquitous software components
- Not limited to one industry
- First capability found before deployment
2025 Threat Statistics
| Metric | Value |
|---|---|
| Known ICS malware frameworks | 7 |
| New ICS malware in 2024 | 3 (half of previous 14 years combined) |
| Critical infrastructure incident increase (3 years) | 668% |
| Hacktivist attacks on US OT/ICS (Nov 2023-Apr 2024) | 36 |
Nation-State Threats: Volt Typhoon
Threat Overview
CISA assesses Volt Typhoon as a PRC state-sponsored actor targeting US critical infrastructure. The US Intelligence Community considers China “the most active and persistent cyber threat” to US institutions.
Targeting Strategy
- Pre-positioning on IT networks for potential future disruption
- Primary targets: communications, energy, transportation, water/wastewater
- Collecting detailed ICS and SCADA documentation
- Maintained access for at least five years in some environments
Techniques
| Technique | Purpose |
|---|---|
| Living off the land | Using legitimate tools to avoid detection |
| Valid accounts | Leveraging legitimate credentials |
| Strong operational security | Enabling long-term persistence |
| KV Botnet | Scaling across thousands of unmanaged devices |
CISA Warning
“Despite the work of CISA teams and federal and industry partners, adversaries remain relentlessly focused on holding critical infrastructure at risk. What has been found is likely just the tip of the iceberg.”
ICS Security Frameworks
NIST Cybersecurity Framework
- Flexible, voluntary, risk-based approach
- High-level guidance suitable for various industries
- 47.8% of critical infrastructure organizations map to NIST CSF
- Functions: Identify, Protect, Detect, Respond, Recover, Govern
ISA/IEC 62443
- International standard specifically for OT environments
- Prescriptive with detailed, actionable guidelines
- Defines secure zones and security levels
- Shared responsibility among users, integrators, vendors
Security Levels:
- SL1: Protection against casual violation
- SL2: Protection against intentional violation with low resources
- SL3: Protection against sophisticated attacks
- SL4: Protection against sophisticated attacks with extensive resources
NERC CIP
- Mandatory for bulk power utilities in North America
- 13 standards covering asset inventory, access controls, incident response
- Required for BES users, owners, and operators
Framework Selection
| Framework | Best For |
|---|---|
| NERC CIP | US national power grid participants (mandatory) |
| NIST CSF | Organizations with mature practices seeking flexibility |
| IEC 62443 | Organizations starting OT security or seeking industry best practices |
Asset Inventory and Visibility
The Challenge
According to CISA’s August 2025 guidance:
- 61% of industrial organizations struggle to monitor critical assets
- 45% of Dragos service engagements lack OT network visibility
- Legacy systems run decades-old software
- Proprietary protocols incompatible with IT tools
Static vs Dynamic Visibility
| Type | Purpose |
|---|---|
| OT Inventory | Detailed, static record of all OT assets |
| OT Asset Visibility | Dynamic, continuous insights into status and security |
Both are essential but serve different purposes.
Best Practices
| Practice | Implementation |
|---|---|
| Real-time inventory | Track all OT devices continuously |
| Network segmentation | Isolate OT from IT and external systems |
| Specialized tools | Use OT-specific visibility tools for legacy protocols |
| Identity-based tracking | Track devices regardless of network location |
| Firmware updates | Regularly update even legacy systems |
Patching in OT Environments
Key Constraints
Legacy systems:
- Substantial OT environments run incompatible legacy systems
- End-of-life systems lack vendor support
- Specialized hardware cannot integrate with modern software
Uptime requirements:
- Strict uptime requirements make downtime costly
- Production disruption leads to economic losses
- Organizations may delay or skip patches
Expertise gap:
- Deep OT knowledge required to avoid unintended consequences
- General IT administrators may not understand PLCs, DCS, SCADA
2025 Statistics
| Metric | Value |
|---|---|
| Internet-exposed ICS device increase (2024-2025) | 40% |
| KEVC entries with vendor workarounds | Only 13% |
| Organizations redirecting budgets to resilience | 62% |
Strategies
When patching is not feasible:
- Virtual patching and compensating controls
- Network zoning and restrictions
- Credential and session management
- Micro-segmentation with IAM
- Cyber deception (decoys)
When patching is possible:
- Develop comprehensive asset inventory
- Prioritize high-severity and remotely exploitable vulnerabilities
- Use limited patching windows effectively
- Test patches in staging environments
- Apply risk-based prioritization
Remote Access Security
2025 Threat Landscape
| Statistic | Value |
|---|---|
| Ransomware attack increase on industrial organizations | 87% |
| OT sites with insecure remote access configurations | 65% |
Unpatched VPNs, misconfigured remote access, and lack of monitoring are primary vectors.
Best Practices
Zero Trust Architecture:
- Replace VPNs with identity-based authentication
- Limit access to specific assets, not entire networks
- Adaptive architectures with behavioral analytics
Access Controls:
- Use named accounts; prohibit shared accounts
- Grant only task-specific access
- Apply MFA per site, per session, per asset
- Implement just-in-time access approval
Network Architecture:
- Broker remote access through DMZ
- No direct inbound connections to sensitive devices
- Additional inspection and logging
Session Controls:
- Require two-step connection via hardened jump host
- Role-based access into OT systems
- Monitor and record every session
- Operators retain control to pause or terminate
Vendor Management:
- Require vendors to use organization’s remote access methods
- Monitor for vendor-installed remote access tools
- Identify unauthorized access with traffic monitoring
ICS Security Tools
Market Leaders (2025)
| Vendor | Strengths |
|---|---|
| Claroty | Comprehensive CPS protection, IT/OT/IoT coverage, integrated secure remote access |
| Nozomi Networks | Strong threat detection, AI-powered analytics, easy UI |
| Armis | Vulnerability management, dynamic segmentation |
| Dragos | Deep critical infrastructure expertise, ICS threat intelligence |
Selection Criteria
| Factor | Consideration |
|---|---|
| Protocol support | Coverage for your specific ICS protocols |
| Deployment model | Cloud, on-premises, or hybrid |
| Integration | Compatibility with existing security stack |
| Threat intelligence | Quality and industry relevance |
| Vendor expertise | Industry-specific knowledge and support |
Building an OT Security Program
Maturity Model
Phase 1: Implementation (Quick Wins)
- Develop necessary skills and resources
- Execute core use cases
- Integrate OT security into IT frameworks
- Set up basic infrastructure
Phase 2: Operationalization
- Execute advanced use cases
- Mature security designs
- Expand to medium-impact sites
Phase 3: Optimization
- Fine-tune cybersecurity measures
- Continuous monitoring and risk management
- Iterative improvements
2025 Statistics
| Metric | Value |
|---|---|
| Organizations at Level 1 (Basic) maturity | 26% |
| Organizations planning CISO oversight of OT | 80% |
| Organizations using 1-4 OT vendors | 78% |
| Organizations incorporating threat intelligence | 49% |
| Organizations redirecting to resilience strategies | 62% |
Core Controls
| Control | Implementation |
|---|---|
| Asset inventory | Complete visibility of all OT assets |
| Network segmentation | Purdue Model implementation |
| Access controls | Authentication and authorization |
| Monitoring | Detection capabilities for OT environments |
| Incident response | OT-specific response procedures |
IT/OT Convergence
Current State
IT and OT are merging across systems, organizations, and policies. Cross-functional teams are being reorganized under shared governance models.
Governance Model
- Establish collaboration between OT and IT teams
- Clarify ownership and roles
- Define responsibilities for hybrid devices (smart meters, digital twins)
Success Factors
| Factor | Implementation |
|---|---|
| Culture program | Convergence is about culture as much as technology |
| Executive sponsorship | High-level support enables acceptance |
| Standards-based architecture | Use frameworks like IEC 62443 for unified approach |
| Shared objectives | Common metrics and performance goals |
Maturity Indicators
- Merged OT and IT security budgets
- CISO visibility to OT security risk data
- OT personnel invited to cloud strategy meetings
- Formal collaboration programs
- Shared performance metrics
Key Statistics Summary
| Metric | Value |
|---|---|
| Organizations with OT incident (past year) | 22% |
| Incidents causing operational disruption | 40% |
| Ransomware surge (YoY) | 87% |
| Manufacturing ransomware victims | >50% |
| Ransomware causing full OT site shutdown | 25% |
| Organizations struggling to monitor assets | 61% |
| OT sites with insecure remote access | 65% |
| Internet-exposed ICS device increase | 40% |
| Critical infrastructure incidents increase (3 years) | 668% |
Implementation Checklist
Foundation
- Conduct OT asset inventory
- Map current network architecture to Purdue Model
- Identify critical assets and processes
- Assess compliance requirements (NERC CIP, IEC 62443)
- Establish executive sponsorship
Network Security
- Implement network segmentation per Purdue Model
- Deploy industrial DMZ between IT and OT
- Secure remote access with jump servers and MFA
- Filter ICS protocols with industrial firewalls
Visibility and Detection
- Deploy OT-specific monitoring tools
- Establish behavioral baselines
- Integrate threat intelligence
- Configure alerting for anomalies
Operations
- Develop OT-specific incident response procedures
- Establish patching strategy for constrained environments
- Train IT and OT personnel on converged security
- Conduct regular exercises and tabletops
ICS/OT security requires understanding that these environments operate under fundamentally different constraints than IT. Availability and safety trump all other concerns. Effective OT security programs work within these constraints while implementing appropriate controls to address the growing threat from nation-states and ransomware operators targeting critical infrastructure.