Large corporate networks scare me.
I was at a plant that had a successful line, and so it was to be duplicated in Shanghai. They sent the PLC and HMI code, all the mechanical and electrical drawings over to the plant there.
Many months later, for no particular reason, a motor on our line started up, even though no one was anywhere near an HMI. As you can probably guess, the Shanghai plant duplicated the system, but didn't change all the IP address. From 7000 miles away, commands from their HMI was getting routed to our PLC, through the business network.