DISCORD SERVER HACKER ALERT

Actually guys today in our server a hacker joined with 1 alt (idk how he/she joined without invite)
he himself enabled rob command without permission how we don't know, he himself robbed everyone in the server and he set himself a custom tag (#0001)without a nitro, we dont know how he joined and how he enabled the dank memer rob command!!
pls discord community look into it 
Screenshots:
First name of when robbing

Name 2 after leaving and joining