In order to help protect from future unauthorized purchases, please secure your device from unauthorized use by implementing a password, PIN or any other security lock your device may have. It would also be prudent to change any passwords for any linked accounts, including your Facebook or Google Play account.

In addition, we strongly encourage you to enable a password or authentication for in-app purchases.  You can find detailed information on how to set this up here:  https://support.google.com/googleplay/answer/1626831