Public phone charging stations seemed like a simple solution to an annoying problem, but as it turns out they’re more of a risk than a solution.

The FBI is warning people of “juice jacking,” where criminals use public chargers to infect phones and devices with malware.

The FBI says that people should not use public chargers at malls and airports and should instead use their own USB cables and charging boxes.

The most recent warning comes from the Denver FBI branch, although they did not point to any recent incidents that would prompt the alert. It does follow similar guidance made on the FBI’s main website.

Devices plugged into “juice jacking” cords can be hijacked and have information stolen through software that can capture user names, passwords and more.