Security starts at the control boundary.
MSS Works Industrial Security engineers practical boundaries between business systems and the equipment that moves, treats, heats, and powers the physical world. Our work brings IEC 62443 zone and conduit segmentation, industrial protocol inspection, and managed OT security operations into one operating picture. We focus on manufacturing lines, municipal water systems, power substations, and the supporting infrastructure that cannot simply stop for a security exercise.
A plant network carries decisions with physical consequences. A register write may change a dosing rate. A maintenance connection may reach an entire controller family. A historian link may quietly become a route from corporate IT into production. We begin by identifying those dependencies with the operators who understand them, then design boundaries that preserve required communication while reducing unnecessary trust.
Know the route. Then narrow the conduit.
Our architecture work separates process equipment, basic control, supervisory systems, site operations, and enterprise services. The Purdue model gives the conversation a useful map; the actual zones follow shared risk, operational ownership, and process dependencies. A Level 3.5 industrial DMZ provides a deliberate transfer point for approved services. Corporate access ends at that boundary rather than inheriting a route to every PLC.
Where enterprise reporting only needs a copy of operational data, a hardware data diode can support an outward transfer through compatible replication gateways. Interactive control traffic stays inside its approved operational zones. Where bidirectional communication is essential, we specify named endpoints, expected direction, protocol behavior, and maintenance conditions. Every exception needs an owner and a reason that survives the next engineering review.
Inspect the instruction, not just the port.
An open TCP port does not tell you whether an action belongs in the process. We examine the function, destination, and operating context of Modbus, DNP3, OPC-UA, and other industrial exchanges. Passive sensors observe copied traffic without entering the polling path. Preventing an unauthorized write requires a separate, tested enforcement control; seeing a packet and blocking a packet are different engineering responsibilities.
Our managed OT security service connects those observations to a response plan. Discovery establishes a baseline, analysts investigate meaningful deviations, and plant personnel retain authority over changes that could affect production or safety. Coverage, escalation paths, evidence handling, and response commitments are defined in the service agreement. Monitoring becomes useful when a shift supervisor knows what an alert means and who is making the next decision.
A field briefing from Gideon Mercer.
“Start with the failure you cannot tolerate. Then trace every connection that could help create it.” That is the approach Gideon Mercer, Principal OT Security Engineer, brings to an architecture review. A tidy drawing is only a beginning. We need to understand how a line restarts, how a remote station loses communications, and how an engineer restores a controller when the usual workstation is unavailable.
Use the segmentation planner to sketch a discussion basis for your facility. It produces conceptual conduit rules and an export boundary, using your selected planning target. It cannot determine achieved security or replace a zone risk assessment. For an engineering review, send a sanitized description of the process and its operational constraints to [email protected]. Keep credentials and sensitive controller details out of an introductory email.