A professional hacker says that anyone with a little time and about $100 can hack into the traffic systems of the world's largest cities.

Cesar Cerrudo told CTV's Canada AM that he's hacked into the traffic systems of Seattle, Washington and New York City just to prove his point.

And now, he's going public with his exploits, as a cautionary warning for those in charge.

"Because these devices are unsecured, it's like anyone can send fake data," he said.

Inspired by the movie "Live Free or Die Hard," he travelled to the U.S. from his home in Parana, Argentina to see how easy it would be to hack into a traffic signal system.

In the movie, terrorists take control of traffic and rail signals, as well as air traffic control, hacking into the systems with just a few strokes on a keyboard.

Cerrudo did some research, and with the help of a device purchased online, he was able to intercept the signal between sensors in the pavement and the traffic control centre in New York City. With that, he could trick the system into changing lights or stalling on red lights.

"They can make the traffic control system believe that, maybe in one direction, there's a lot of traffic (when) there isn't," he said.

And that could prove dangerous if, for example, the signal changes instantly from green to red. Without the amber warning, the risk of collisions would be much higher. A hacker could also stall a major intersection at rush hour, leaving a light red for hours.

Cerrudo mounted a Sensys Networks wireless transmitter to a drone, and found he could intercept data being fed to traffic control systems from 50 metres away.

He then attached an antenna to the USB-drive-sized transmitter and found he could be 500 metres from a light and still intercept the data.

"You have to be a professional (to build a hacking tool), but after you implement an attack in a tool then anyone can use that tool," Cerrudo said.

The Sensys Networks vehicle detection systems are installed in 40 U.S. cities, including New York, Los Angeles and Washington, D.C. They're also used in Australia, France, Canada and the U.K.

Toronto uses Siemens' SCOOT system, which detects traffic from sensors under the pavement then relays information to a data centre. It's similar to the Sensys system, and though it hasn't been hacked yet, it could be targeted in a similar way.

Cerrudo will be presenting his findings at a conference in Florida on May 15.