>prevent unauthorized devices

Again, STUXNET shows that bugs get into authorized devices really easily. One of the biggest issues is you have power guys that don't know dick about computer security using fleets of laptops that will need a huge amount of training to bring them up to the needed high levels of security.

More so there are thousands of these devices out in the field in power company trucks. All it takes is someone picking one of these up and infecting it for the problems to spread.

It is an insanely hard problem to solve. Breaches happen in military networks pretty often. As a measure of secrecy, they never tell you about it.