A programmable logic controller (PLC) is an industrial computer that runs stored instructions to control connected equipment. In a water facility, for example, signals from sensors can help a PLC decide when to switch a pump or valve. Because such controllers can participate in real operating processes, unauthorized access may interfere with operations—but a PLC compromise does not automatically mean unsafe water or an outage.
What a PLC does
NIST defines a PLC as “A solid-state control system that has a user-programmable memory for storing instructions for the purpose of implementing specific functions such as I/O control, logic, timing, counting, three mode (PID) control, communication, arithmetic, and data and file processing.” NIST’s glossary gives the formal definition.
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In plain terms, a PLC repeatedly receives signals from connected equipment, runs its programmed logic, and changes outputs according to those instructions. A sensor might report a measurement; the controller evaluates it against its programmed rules and can send an output to attached equipment. The exact inputs, logic, and actions depend on the installation. Unitronics describes this input-processing-output pattern in its PLC overview.
How a PLC differs from an HMI and SCADA
A PLC executes control logic and works with equipment inputs and outputs. A human-machine interface (HMI) is the operator-facing interface used to view information and interact with a system. Supervisory control and data acquisition (SCADA) refers to supervisory monitoring and control systems. These terms describe different roles, not interchangeable names for one device.
#1 Best Overall
- -- PLC Type: Fully compatible with FX1S, 7 Input 5 Relay Output (24V pulse single). Have additional 4 Transistor Output: 2 for high speed pulse 100KHz & 2 for direction, can drive 2 servos or 2 steppers with pulse
- -- PLC software: Use GX Workers 2 or Developer (pls download from GX Workers 2 website, we only have Chinese version), support Command + T Ladder Diagram + SFC for programming
- -- HMI Software: YKBuilder V5.3/7.0 (Pls contact us, we will share it and the video instruction and guidelines). For HMI model: pls choose FE Serial, 280D
- -- Use the same Cable for download program from PC to PLC/HMI: Use the: mini port – USB cable, pls install HMI & PLC’s USB driver first, which we will share.
Some products combine PLC and HMI functions in one unit. Unitronics’ Vision700 is an example. Whether functions are integrated or separate, a PLC may be one component within a larger operational technology (OT) environment that includes other controllers, operator interfaces, and supervisory systems.
Why PLC security matters to water utilities
Water and wastewater systems rely on both information technology (IT) and OT. OT includes the systems involved in monitoring or controlling physical processes. If an attacker gains access to a vulnerable controller or related OT, that access could be used to manipulate controls or interfere with operations.
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- Weight: 1.00lb
- Product Dimensions: 9.00 x 9.00 x 7.00 inches
- Condition: New
The U.S. Environmental Protection Agency advises drinking water and wastewater system owners and operators to assess cyber risks to both IT and OT, identify weaknesses, and plan measures to reduce risk. EPA warns that malicious activity against vulnerable OT could disrupt production of clean and safe water. That is a potential consequence—not proof that every cyber incident changes water quality or interrupts service. The outcome depends on the utility’s process, system design, safeguards, and the access an attacker obtains. See EPA’s water-sector cybersecurity guidance.
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What the Unitronics attacks demonstrated
A joint advisory from CISA, the FBI, the NSA, EPA, and international partners says actors affiliated with Iran’s Islamic Revolutionary Guard Corps, using the CyberAv3ngers persona, began targeting Israeli-made Unitronics Vision Series PLCs and HMIs in November 2023. The advisory says such devices are used in water and wastewater facilities and other sectors, and reports that affected devices were accessed over the internet using default or no passwords. The original advisory was published December 1, 2023, and revised December 18, 2024; its chronology is not evidence of newly discovered attacks in 2026. Read the joint advisory.
Rank #3
- -- PLC Type: Fully compatible with FX1S, 10 Transistor Input (NPN Type), 7 Relay Output. Have additional 4 Transistor Output: 2 for high speed pulse 100KHz & 2 for direction, can drive 2 servos or 2 steppers with pulse, built-in 2AD（0-10V) and 2DA(0-10V), also 2 NTC10K B3435 probe. Just read the address of AD DA NTC's will ok, 2 high speed input 100KHz X0 X1 to control encoder
- -- PLC software: Use GX Workers 2 or Developer (pls download from GX Workers 2 website, we only have Chinese version), support Command + T Ladder Diagram + SFC for programming
- -- HMI Software: YKBuilder V5.3 and Choose FE serial 380 model in HMI software. (Pls contact us, we will share it and the video instruction and guidelines), very easy to use, just create the buttun and set the address
- -- Use the same Cable for download program from PC to PLC/HMI: Use the: mini port – USB cable, pls install HMI & PLC’s USB driver first, which we will share.
The case illustrates why internet exposure and weak authentication can matter. It does not establish that PLCs throughout the water sector have been compromised, nor that every affected device caused a service disruption or water-quality problem.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Security priorities for water-sector OT
Federal guidance recommends that utilities evaluate controls in the context of their own systems rather than treat any single measure as a complete solution. CISA, EPA, and the FBI’s February 21, 2024 fact sheet groups practical actions across exposure reduction, assessment, credentials, asset management, response, backups, vulnerability reduction, and staff training. The recommendations below reflect that guidance and the joint advisory.
Rank #4
- -- PLC Type: Fully compatible with FX1S, 10 Input 7 Relay Output (5V pulse single). Have additional 4 Transistor Output: 2 for high speed pulse 100KHz & 2 for direction, can drive 2 servos or 2 steppers with pulse; have 2 high speed input 100KHz X0 X1 to control encoder also
- -- PLC software: Use GX Workers 2 or Developer (pls download from GX Workers 2 website, we only have Chinese version), support Command + T Ladder Diagram + SFC for programming
- -- HMI Software: YKBuilder (Pls dowload from link or contact us, we will share it and the video instruction and guidelines), very easy to use, just create the buttun and set the address
- -- Use the same Cable for download program from PC to PLC/HMI: Use the: mini port – USB cable, pls install HMI & PLC’s USB driver first, which we shared from link
Reduce exposure and control access
- Remove unnecessary direct public-internet access to PLCs and other OT. If remote access is needed, put controlled mechanisms such as a VPN, gateway, proxy, or firewall in front of OT, and use multifactor authentication (MFA) for OT network access where applicable.
- Replace default or weak passwords on PLCs and HMIs. Require authentication for access to field controllers and for changes to them.
- Segment networks and use firewalls and controlled connections appropriate to the environment, so access to one zone does not automatically grant access to control assets elsewhere.
Know what is connected and keep it maintained
- Maintain an inventory of IT and OT assets, including their purpose, internet exposure, and patch or support status.
- Keep controller firmware and engineering-workstation software current according to manufacturer guidance and security advisories applicable to the specific model.
- Assess cyber risks periodically and train staff who operate, maintain, or support the systems.
Detect changes and prepare to recover
- Monitor for unusual logins and remote access, as well as unexpected changes to device configuration or control logic.
- Back up PLC logic and configurations, and test that the backups can support recovery.
- Develop and exercise incident-response and recovery plans for OT and IT systems.
CISA, EPA, and the FBI published their eight-action water-sector fact sheet on February 21, 2024; its recommendations are a practical starting point, not a substitute for assessing a facility’s architecture. Read the fact sheet. CISA and EPA also announced a water-sector cybersecurity toolkit on February 7, 2024, with resources for utility owners and operators: CISA’s announcement.
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