it's called referrer spam. they've been doing it for years and years, as people seem to find some reason they want their referrer list publicly viewed -- thus it's a great place to spam links.
1. don't show your referrals publicly (not saying you are, this is general consumption...). usually attacks are when there's an active referral listing somewhere.
2. use a referral-spam blocker. CG-Referrer (which also does lots of stats stuff and breakdowns of searches, bots, feed reading, etc.) does a good job, and I'm certain that other things (Bad Behavior comes to mind) would alleviate the issue as well. I've got a new version of CG-Referrer I'm working on that will do much better than my last release...