It's possible the company who made the industrial machinery used an "Indiana Jones film booby trap" and a kernel level anti-cheat system from the AAA GameDev industry to detect debuggers being attatched and deliberately damage the expensive factory machinery you bought from them so that you would have to pay them to repair it. But would such a technically capable company produce a controller using an Excel spreadsheet and Visual Basic? Seems more likely that it would be a fairly pedestrian C dll written by electrical engineers with an RS-232 interface and logic for reading/writing stepper motor state and temperature sensors.
Anyway, I didn't suggest debugging it live. "Can Claude code just from DLLs?"[1] - "You could've just pasted the DLL into Claude by now and had the results. Claude can read and analyze basically anything" and "Claude has done that a lot for my projects. Doesn't matter if it's a dll built with .NET or C, etc. Claude just figures it out, somehow."
Even if you don't start with `strings` and a decompiler and whatever, it would take less time to copy the spreadsheet and DLL into Claude and prompt "what can you make of this? What are the major functions in the DLL, when does it do writing vs polling? What else does it do?" than it would take to write a breathless dramatic comment on HN about how Mission Impossible the task is.
But ok let's say it was built by villains and it is booby-trapped and the DLL is encrypted, password protected, hardware dongle verified, but somehow still on Windows XP or whatever, and it is impossible to even copy or take a backup - plug the cable into a logic analyzer on its way to the machinery and capture the wire protocol. It's likely using a standard old-school serial connection with a known protocol and no encryption or verification. It's not like they need to tap a 1.5Tbps undersea fibre bundle.
[1] https://old.reddit.com/r/ClaudeAI/comments/1x28deo/can_claud...