1. User 1 Logins to Minecraft
2. Play minecraft, Check your which world are yours
3. Log out. Close Minecraft
4. Login as User 2.
5. Create a world and play.
6. Log out.
7. Log in as user 1. Now you see User 2 world.
8. You can delete or change things in User 2 worlds.
9. When user 2 logins, the changes are still there.

Do you provide bug bounties?