Well, just removing the links might stop the average joe from using the standard registration method.
But for someone with some knowledge this will not be a real problem.
yes you would have to mod reg.php to only work if "user signing up has a reffer"
But you know there is a bug or spelling error in vb right to 3.0.6
if you make a spelling mistake in the refferer box it says "User name doesnt exist"
anyone with a brain assumes they are talking about them... ever tried that?