Referrer spam

Referrer spam is a kind of spamdexing (spamming aimed at search engines). The technique involves making repeated web site requests using a fake referrer url that points to the site the spammer wishes to advertise. Sites that publicize their access logs, including referrer statistics, will then end up linking to the spammer's site, which will in turn be indexed by the search engines as they crawl the access logs.

This benefits the spammer because of the free link, and also gives the spammer's site improved search engine placement due to link-counting algorithms that search engines use.