O’FALLON, Mo. (CBS/AP) – As users of the hottest new smartphone game Pokemon Go try to catch ‘em all, police are warning players to watch their backs.

The “augmented reality” game, which layers gameplay onto the physical world, became the top grossing app in the iPhone app store just days after its Wednesday release in the United States, Australia and New Zealand. Players already have reported wiping out in a variety of ways as they wander the real world — eyes glued to their smartphone screens — in search of digital monsters.

Related: Viral Photo Shows Pokemon Go Bringing Police, Young People Together

But in addition to tripping over sidewalks, walking into trees and wandering through busy intersections, authorities say there’s also a risk of players becoming the targets of criminals.

In Missouri over the weekend, four young men charged with armed robbery are accused of using the Pokemon Go app to target their victims.

“Pokestops,” where players can go to collect items like Pokeballs, are popular gathering spots in the game and in real life. That’s where the suspects were waiting, police say.

“Apparently they were using the app to locate ppl standing around in the middle of a parking lot or whatever other location they were in,” the O’Fallon Police Department said. “If you use this app (or other similar type apps) or have children that do we ask you to please use caution when alerting strangers of your future location.”

Police in Massachusetts are also getting wind of the app. Woburn Police Chief Robert Ferullo sent a tweet Sunday urging players to “make good decisions.”

Please make good decisions if you are playing Pokemon GO, stay aware of your surroundings and have fun !! pic.twitter.com/ltnEM699Zd — Chief Robert Ferullo (@ChiefFerullo) July 10, 2016

And in Northbridge, authorities are asking users to stay off private property, don’t walk in the road while playing, and don’t Pokemon Go and drive.

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