Dawn had the same problem. Read this topic to see how she handled it.
http://www.pixelpost.org/forum/viewtopic.php?t=1625
It's also been discovered that 1.4.2 doesn't fully stop referer spam:
http://www.pixelpost.org/forum/viewtopic.php?t=1667
My advice, check out the first link I mentioned. It has a bunch of hints on stopping spam completely.
Finally, the granddaddy for referer spam discussion is here:
http://www.pixelpost.org/forum/viewtopic.php?t=1252