After getting the admin access in the website attacker will upload his own control penal 

that’s called shell. It helps attacker to maintain access for the long time. There are many 

types of shells like DDOS shell, symlink shell etc.

Using shell attacker can destroy whole database and he can leak the database of the website 

and using the shell he can root the server. (Only Linux server can be rooted windows server 

cant be rooted because there is no ROOT :P) After rooting he can destroy whole server. 

Suppose One server contains 500 websites and attacker got the admin access in the single 

site and he have rooted that server then 500 sites can be destroyed !
USES OF SHELL

1. Using shell you can Destroy the INDEX page of the website.
2. You can host your files in the Server.
3. You can root the server.

Now if you want to destroy the index page of the website then find the “INDEX” page from 

the list and replace that coding with your own deface page. And using browse option you can 

host your own file in the server. You can create your own shell and you can add your own 

tools in your shell for that you know PHP.