This brave new world of Pokémon gaming can be surprisingly dangerous.

Pokémon Go launched for mobile in the U.S. on July 6, and it has immediately become a hit. However, some people are using the location-based game for disturbing reasons. Specifically, muggers have used Lures (which make Pokémon more likely to appear in a specific location) to attract potential victims. The people behind Pokémon Go are urging its players to be careful.

“We are aware that some incidents have occurred involving fans playing Pokémon Go,” The Pokémon Company and developer Niantic told GamesBeat in a joint statement. “We encourage all people playing Pokémon Go to be aware of their surroundings and to play with friends when going to new or unfamiliar places. Please remember to be safe and alert at all times. We are humbled by the overwhelmingly positive response to Pokémon Go and greatly appreciate the support of our fans.”

The muggings happened on July 10 in O’Fallon, Missouri.

We’ve had location-based games before (including Niantic’s own Ingress), but none have rocketed to popularity like Pokémon Go. Its success will bring about new questions about safety while gaming.

Just remember that if you plan to walk around and catch some Pokémon, try to do it with friends and in public, safe places.