Guests cannot see links

[sajjid]

can someone make a plugin so guests cannot see links in the posts instead they see a message " you must register to see the link".
thanks
this code can be found in forums/oncludes/class_bbcode.php

return "<a href=\"$rightlink\" target=\"_blank\">$text</a>";

if i replace to this

this hides the link for everyone but i want to hide it to guests only.

global $bbuserinfo; 
if ($bbuserinfo[userid] != 0) 
{ 
return "<a href=\"$rightlink\" target=\"_blank\">$text</a>";
} 
else 
{ 
return "Guests cannot view links. You must <a href='register.php'>register</a> to see links.";