An experiment by Berlin-based artist Simon Weckert has revealed how the navigation application Google Maps can be hacked.

According to Weckert’s blog, 99 second-hand smartphones were placed in a handcart that was dragged through visibly empty streets to generate a virtual traffic jam in Google Maps, and it worked. Google Maps marks streets with heavy traffic in red colour that was observed in areas where the handcart was moved through.

“Through this activity, it is possible to turn a green street red which has an impact in the physical world by navigating cars on another route to avoid being stuck in traffic,” the blog said.

Google Maps is believed to use the density of smartphones connected to the internet – specifically, Google – as a proxy for the density of traffic.