When it comes to critical national infrastructure, the highly distributed and ultra-interconnected U.S. power grid is, hands down, the most vulnerable to cyberattack. On this one point, many cybersecurity experts seem to agree.

Internet warfare: Is the focus on the wrong things?

Yet just how likely a terrorist target is the grid? And what's the best way to secure and protect the massive inventory of generators, power plants and transmission lines plus the cat's cradle of computer networks that make up the electric power system?

Talk to 10 experts, and you'll likely get 10 different answers.

"The problem is that we have a hard time assessing risk," says Jim Lewis, a senior fellow specializing in cybersecurity at the Center for Strategic and International Studies. "We seem to settle on either indifference or a Bruce Willis movie."

Up until about a decade ago, things were a lot simpler. The industrial control systems that manage the generation and flow of power were pretty much protected from intrusion by their closed-loop architecture. These control systems existed and operated in isolation from everything else.

But increasingly, these systems have been linked to countless corporate networks for everything from real-time monitoring of electricity generation and transmission to remote meter reading and automated grid operations.

"We had an explosion in business network technology, and as that occurred, individuals in accounting, for example, wanted real-time information at their desktop computers so they could do projection planning," says Michael Assante, chief information security officer at North American Electric Reliability Corp. (NERC), an industry organization of U.S. electrical grid operators.

The smart grid relies heavily on public communication networks, including cellular networks and WiMax, to digitally monitor and control the grid for more efficient operation, he explains.

More vulnerability

But more connections mean more points of vulnerability, and that's what worries Sami Saydjari, president of Cyber Defense Agency, a privately held security consulting firm headquartered in Wisconsin Rapids, Wis.

"The power grid is controlled by systems that are antiquated and highly vulnerable because they have very little security. They've been historically protected by disconnection," he says.

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