... Who the fuck is putting this shit on a network that's not closed circuit?
Two things worth keeping in mind:
1. Connecting them was probably considered best practice when they were installed in 2005 2. Their support contract required them to stay connected
Vendors install these so the store owner and them have easy access to alarms and controls.
A VPN per store would be too complex for the vendor so they just expose these to the open.
Same story as with all the hacked OT/SCADA systems in the past.