Once in the network, an attacker would not be able to switch lights to red, green and yellow. A safety feature called a malfunction management unit and required in all controllers is hardcoded to know all the safe patterns for traffic lights.
Trying an unsafe configuration would automatically send the light to blinking red. Therefore, a hacker would be limited to changing lights to red.
Nevertheless, a city filled with red lights would cause major traffic jams and chaos on the streets. To fix the mess, city workers would have to go to each intersection to reset the lights.
"The cost would be real in terms of man hours and money, but it wouldn't be as dangerous as a four-way green light would be," Ghena said.
Whether other towns and cities would be susceptible to the same attack would depend on their individual security mechanisms.
"There's lots of little simple things you can do to improve your security," Ghena said. "But to really fix the problem involves the standards organizations and the vendors getting together and really trying to make sure their systems are designed with security in mind."
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