I believe s/he meant if the box you are using to log in is compromised, then all boxes your box has access to (by way of the private key it has in its file system) are compromised, whereas it seems you interpreted the comment to be implying that the host to which you are logging in (which only has the public key in its file system) has been compromised.<p>The point is that the computer on which you type becomes a lynch-pin.