Head Ball 2's account security is provided by Google Play, Game Center and Facebook. People with Google Play Games or Facebook accounts can access your Head Ball 2 account.
To ensure the security of your accounts, do not share the password of your Google Play Games and Facebook accounts to avoid losing your Head Ball 2 account. If you get your Google or Facebook account information stolen, it would be impossible for us to help you as Masomo.
Remember to change your passwords regularly and ensure your accounts' security.
If you have shared your account once, another user or users can log in to your account even if you change your password. Unfortunately, we cannot help you with this in any way.