my server got hacked?

my server got hacked? helppppppppppppppppp !

My server got these problems:
- the folder "public_ftp" got permission 000 and owner change to be 0
- my cpanel password got changed
- it's happened on 2 websites with the same problem above
- while go to homepage IE show msg 404 errors file not found ( all files inside "public_html" is full with same files and permission )

Primary questions:
- how he can do this?
- how can i resolve this problem? and how to prevent it?

Secondary questions:
- which user access can do this thing? If not SSH root access.
- is this weakpoint of cpanel then he can attack my server?


Thank You ~

 

He came to clear any log files.