Distributed COM (DCOM) is a Microsoft technology that provides Windows applications with the ability to connect from one computer to another on a LAN, a WAN, or an Internet connection. For example, DCOM allows the OPC Classic (DA, A&E, HDA) client application to communicate from one computer to the OPC Classic server on another computer. OPC UA does not use DCOM. It is important to understand the details around DCOM security to ensure OPC Classic works properly using DCOM.
DCOM Hardening:Microsoft KB5004442 makes changes that require minimum security levels when using DCOM on Windows Operating Systems that receive the patch. Starting with the June 2022 Windows Updates Microsoft will enforce the higher security by default, with the ability to disable through a registry entry, and in March 2023, the higher security will be mandatory and cannot be disabled. Read more in our DCOM Hardening Technical FAQ. Anything stated there supersedes any conflicting instructions in our DCOM tutorials.