Hackers have found yet another way to cause chaos for the government. Branden Ghena, an electrical engineer at the University of Michigan had his team conduct an experiment to see just how safe traffic lights are. While it might be hard to grasp, Ghena proved that traffic lights are just as vulnerable as your gmail account.
According to newscientist.com, there is a controller switch present at every intersection that can be set to change at regular intervals or based on input from external sensors (hackers). These controllers are networked across cities and recieve commands based on data packets.
In short, All Ghena had to do was figure out which sequences of packets corresponded to which controller commands, and he gained full control.
If this seems like it came directly from a movie, you are correct. Remember in the Italian Job, when Seth Green deliberately changed the traffic light system so they could get away with a bank robbery? Well maybe this isn't so far off...