title: How to prevent from Firebase Attack Database ? (More than 100 anonymous account created in one day)
body: <p><br/>
  I have never made any promotion,ads,... for my app. <br/>
  On my Google Play Developper account, I got 31 active installations. <br/>
  During the last 5 days, I got more than 150 anonymous accounts created (100 on 7 October). I suspect someone creating lots of account.<br/>
  I put an event ("account_created") each time an account is created. This event was triggered only 40 times.<br/>
  All the activity seems to be from Puerto Rico.<br/>
  Some of these account appear only in tab "Authentification" but not in my database.<br/></p>
  
  <p>How can I prevent from this to happend next time? <br/></p>
  
  <p>And How can I bulk delete these fake accounts from "Authentification" <strong>and</strong> from my database (These are define by their FirebaseId as primary key).<br/></p>
  
  <p>Thanks a lot</p>