The Pokemon Go app has now been released in the UK amid warning from a children's charity over its safety standards.
The NSPCC have said it is concerned that "basic safety standards appear to have been overlooked".
In the game, players travel around the real world to capture and train creatures known as Pokemon.
The NSPCC is concerned that offenders could target unsuspecting children by using the app's geolocation feature.
Peter Wanless, the charity's chief executive, has written to its developer Niantic, and said: "I urge you to urgently reassess your app and its security and safety features.
"We all have a responsibility to ensure that children are protected and as creators of a game with substantive reach, you have a weighty responsibility to protect your young users."
The app was first launched in Australia and New Zealand before overtaking Tinder in the US in popularity.
The game is proving a hit with millennials who can relive their childhood - the original game was released in 1995 - by catching Pokemon characters using the app.
Mobile provider EE revealed today that more than 350,000 people on its network in the UK have already been using the app before it appeared on the App Store.
Developer Niantic said earlier this week the game's release in the UK would be delayed until they were "comfortable" their servers could handle demand.
The app, which is free to download, has already raised some concerns over claims it could access a user's entire Google account, including email and passwords.
Niantic quickly responded, claiming the move was unintentional, reassuring users that it was not collecting any exceptional data.