I've been working with these systems since the early SCADA (Supervisory Control And Data Acquisition) types of the mid-'80s. At that time it was either leased lines or radio linked. The electric companies usually ran low frequency carrier signals over the power lines themselves, as well as railroads using the track rails on some systems.
Throughout the late '90s these migrated to IP based protocols that were somewhat standardized by Johnson controls and Siemens. This eliminates the safeguards of isolation and proprietory signalling formats that the old stuff had.
The Utility industry is well aware of this issue for some years and the systems are being updated to secure them. Kinda like the nightmare that Microsoft went through when "always on" DSL and cable inernet service became commonplace as opposed to dial-up.
Since it involves hardware changes to some rather pricey stuff it won't happen overnight, but it's also not as bad as the end of the world picture the press always tries to paint.
