It’s only been out for just over a week, but Pokémon Go is already the biggest mobile game in US history; its near 21 million daily active users beating Candy Crush’s peak US DAU of 20 million.

The game’s success means that the appearance of malicious software looking to capitalize on its popularity is inevitable. But what comes as something of a surprise is that three of these apps found their way onto the official Google Play store.

Discovered by security firm ESET, the worst of the three fake applications,“Pokémon Go ultimate,” is the first ever fake lockscreen app to appear on the Android marketplace. Once downloaded, the app appears as “PI Network” and uses a different icon to the one seen on the store.

Launching PI Network will freeze a screen with an image of Pokémon Go, leaving victims the options of removing their battery or using Android Device Manager to restart the device. After rebooting, however, the app continues to run in the background, clicking on porn ads to generate revenue for its creators.

“This is the first observation of lockscreen functionality being successfully used in a fake app that has landed on Google Play," wrote Eset researcher Lukas Stefanko. "It is important to note that from there it takes just one small step to add a ransom message and create the first lockscreen ransomware on Google Play."

In the short time it was available, PI Network was downloaded between 500 and 1000 times before Google removed it from the store.

The two other fake apps, "Guide & Cheats for Pokémon Go" and "Install Pokémongo," use scareware ads designed to trick people into signing up to expensive unnecessary services. Not only will these apps happily steal your personal data, but they’ll also display popups claiming a device is infected with malware and that signing up to a fake virus removal service is only way to get rid of it.

While all three applications have now been removed, they serve as a reminder to fully inspect apps - even those that come from the Google Play store - to make sure they're safe before downloading them.

Image Credit: Randy Miramontez / Shutterstock