How can I prevent users from copying from the TextArea

I have used the CKEditor as a HTML editor in my application, however I got a troublem when I tried to prevent users from copying contents to clipboard for some security reason. I tried to modify the toobar and removed the COPY menu both in Toolbar and ContextMenu. But the "CTRL + C" seems always useful in edtior. Would anyone tell me it is possible or not?

Any reply will be appricaited.

Thanks.