According to ESET, fake Pokemon Go apps have been spotted on the Google Play Store since the game launched. For example, "Pokémon Go Ultimate" looks like the official app, but after installation the app it renames itself to "PI Network." Launching it immediately causes a user's device to lock up, rending the phone useless until the battery is removed or the device is rebooted via the Android Device Manager. Once the phone reboots, the app hides itself and generates ad-revenue by silently clicking ads in the background. Other fraudulent Pokemon apps briefly surfaced that produced fake security messages, attempting to trick users into paying for a virus removal service that doesn't exist. As of this moment all the fake apps have been removed from Google Play. With that being said you should still be on the look out because more are likely to pop up.