Econolite’s traffic lights are used in 100,000 U.S. and Canadian intersections, although it’s unclear if all of those systems are susceptible to hacking.

The problem extends beyond just Econolite — the U.S. traffic light communications standard, called “NTCIP 1202,” is present in all modern signal systems. They can all be hacked if cities don’t change their default settings.

Researchers said that the lights can be made much more difficult to hack with little effort: Guard the network. Cities that install the traffic control systems can enable encryption and set passwords for their networks — both options are available on the Econolite systems. It’s as simple as clicking on a box on the device’s screen.

But that isn’t likely to happen anytime soon. Local governments are cash-strapped and aren’t easily convinced they must manually update every signal controller, said Adam Pridgen, a security consultant at Praetorian.