Three major weaknesses existed: unencrypted wireless connections, the use of default usernames and passwords, and vulnerable dubugging ports—meant that the researchers were able to take control over the lights with a normal laptop. As long as the wireless card in the hacker's computer can communicate at the same frequency that the traffic lights use (5.8Ghz), it can break into the wireless network that powers the entire system.
Scary considering we're putting more and more devices online, but the people doing it don't even put the most basic security practices in place.
If that doesn't scare you… this sort of thing goes all the way up to the most frightening of things: The launch code for US nukes was 00000000 for 20 years… no really: http://arstechnica.com/tech-policy/2013/12/launch-code-for-us-nukes-was-00000000-for-20-years/
Traffic Light Study Reveals Serious Hacking Risk | MIT Technology Review
Security flaws in a system of networked stoplights point to looming problems with an increasingly connected infrastructure.