Could hackers take down a city? Experts say it's no science-fiction fantasy

First the power goes out. It's not clear what's gone wrong, but cars are starting to jam the streets - the traffic light are down. And something seems to be going haywire with the subways, too.

No one can get to work. And even if they could, what would they do? A cyberattack has driven the city to a halt.

Of course, that hasn't happened yet - and to a lot of people the idea of malicious hackers taking down a city still sounds like a bad movie plot. But it may not be as crazy as it sounds, according to security experts who say cities' increasing dependence on technology and the haphazard ways those systems sometimes connect could leave them vulnerable to someone looking to cause chaos.

Cities, like the rest of the world, now rely on a lot of computers. But the systems used to make even the most sensitive systems run can still contain security flaws. While the risk of an actual attack may not be imminent, the threat is looming large over cybersecurity researchers who warn that local governments aren't prepared.

"The potential attack surfaces of a city is a huge challenge," said David Raymond, deputy director of Virginia Tech's IT Security Lab. "The digital pathways between all of the entities and organisations in a city is often not well managed."

Researchers have already discovered vulnerabilities with new technology being used in many cities.