It seems that decades-old technology, such as that proposed for the "new" PATH line, makes it very easy for these intruders. In addition, unmanned substations, like PATH's proposed "death site" in Mt. Airy, are also an infiltration point.
While the power companies pursue outrageous profits creating "new" transmission, they continue to ignore the existing threats posed current infrastructure. As gigantic new "backbone" lines further complicate and interconnect the grid and eliminate local generation on the east coast, we set ourselves up as the perfect target whereby a careless hacker can take the entire east coast off line in an instant.
PATH = not smart!