Referrer spam (also known asreferral spam,log spam orreferrer bombing) is a kind ofspamdexing (spamming aimed atsearch engines). The technique involves making repeatedweb site requests using a fakereferrerURL to the site the spammer wishes to advertise.[1] Sites that publish their access logs, including referrerstatistics, will then inadvertently link back to the spammer's site. These links will beindexed bysearch engines as they crawl the access logs, improving the spammer'ssearch engine ranking.[2]
At least since 2014, a new variation of this form of spam occurs onGoogle Analytics. Spammers send fake visits to Google Analytics, often without ever accessing the affected site. The technique is used to have the spammers' URLs appear in the site statistics, inducing the site owner to visit the spam URLs. If the spammer has never visited the affected site, the fake visits are also calledghost spam.[2]
Techniques for mitigating referrer spam include blocking spamcrawlers and filtering out known spam domains in analytics software.[3] The open-source analytics companyMatomo maintains apublic domaincrowdsourced list of spam-associated domains which it uses in automatic filters.[4]