Referrer spam

The technique involves making repeated web site requests using a fake referrer URL to the site the spammer wishes to advertise.

These links will be indexed by search engines as they crawl the access logs, improving the spammer's search engine ranking.

[2] At least since 2014, a new variation of this form of spam occurs on Google Analytics.

Spammers send fake visits to Google Analytics, often without ever accessing the affected site.

[3] The open-source analytics company Matomo maintains a public domain crowdsourced list of spam-associated domains which it uses in automatic filters.