|This article's factual accuracy may be compromised due to out-of-date information. (May 2015)|
||This article possibly contains original research. (July 2010)|
Referrer spam (also known as 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 referer 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. This technique does not harm the affected sites, just pollutes their statistics.
This benefits the spammer because the free link improves the spammer site's search engine ranking owing to link-counting algorithms that search engines use.
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.
It is found that while some referrer spam pollutes analytics statistics directly, some spammers actually hit the web server. Filtering referrer spam from analytics tools will hide it from the reports but can still continue to consume server bandwidth. To save server bandwidth spammers can be blocked using for example a .htaccess file.
Because the 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.
- Abbatiello, James (27 December 2011). "RefControl". Retrieved 2013-11-19.
- Referrer Spam blacklist Community-contributed list of referrer spammers under Public Domain
- Semalt, Darodar and other Referrer Spam Explained - Technical overview of referrer spam in Google Analytics: how it happens and what you can do
- Malicious Google Analytics Referral Spam Understanding the issue in Google Analytics and security recommendations.