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Referrer spam (also known as referral spam, log spam or referrer bombing) is a kind of spamdexing (spamming aimed at search engines). The technique involves making repeated web site requests using a fake referrer URL to the site the spammer wishes to advertise. Sites that publish their access logs, including referer statistics, will then inadvertently link back to the spammer's site. These links will be indexed by search engines as they crawl the access logs, improving the spammer's search engine ranking. Except for polluting their statistics, the technique does not harm the affected sites.
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. The technique is used to have the spammers' URLs appear in the site statistics, inducing the site owner to visit the spam URLs. When the spammer never visited the affected site, the fake visits are also called Ghost Spam.
As with e-mail spam, referrer spam may be filtered or blocked. A website operator may mitigate referrer spam by preventing search engine spiders from crawling the site logs by moving them to a non-public area such as a password-protected area, by using a robot exclusion file, or by appending the nofollow value to the links.
Referrer spam may also affect third party analytics statistics depending on how the page is accessed. Spammers can actually load the web page content from the target web site (web server), instead of just making a request for the web page (to make it appear in the access log file) and not retrieving the actual web page content from the web site. Filtering referrer spam inside of third party analytics tools can hide it from analytics reports, but it can still have the negative impact of consuming server bandwidth. To prevent this misuse of server bandwidth, spammers can be blocked using various techniques, such as blocking based on a blacklist of IP addresses when an access attempt is made to the web server for a web page.
.htaccess solutions require technical expertise, several developers have created tools for non-technical people to block the spam more automatically, specifically for Google Analytics.
- "Referrer Bombing has caused some of my sites to instantly disappear from google SERP". 22 September 2009. Retrieved 2013-11-19.
- Referrer Spam Blacklist by Piwik - a Community-contributed list of referrer spammers under Public Domain (550+ domains, October. 2017).