Don't worry about it. It is called referral spam, and there is nothing you can do about it. The REFERER header is faked, so there aren't any actual links to your site.
They do this because some people make their referral information public. If the spammers send out millions of fake referrals, all these sites get web exposure. The result is a better Google ranking, etc. You will find all sorts of marketing companies, political compaigns, and financial corporations appearing in your logs and stats, and they are all faked.
It is extremely annoying, of course, because they saturate your logs and make it harder to glean useful information about the data.
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