cannot remove hacker's file
 

A hacker has modified some system files in /etc. I could not find the way to remove (or modify) this file.

I have tried rm -f <filename> with supervisor priviledge (login as root) and got back the msg : "operation not permitted".

Pls. kindly advise

what are the permission levels on the files..? not sure if that will help or not, or can you change the permission levels then try to delete them.

is the security level the same as file permission mode. If so, it is rwxr-xr-x i.e., root should be able to delete it.

if the security level is different from file permission mode, pls. advise how to check it.

If its got spaces you have to quote em to remove them.
rm -f "/path/to/file/file name "
OTOH, if its not in the spaces try
lsattr /path/to/file/filename
to see if the u(undeletable) and i(immutable) bits have been set. If so,
chattr -iu /path/to/file/filename
will remove them, check with lsattr, then try to remove.

*Note there quite possibly are backdoors or compromised services installed. Unless you can *100%* verify the system is ok, I suggest you save your *human readable userdata* only, and reinstall from scratch.

(deleted) Excuse me