A referrer is the location (URI) from which a user has linked to a webpage, for example from another webpage such as a search result.
In the HTTP Standard (at a code-level) referrer is misspelt: ‘referer’.
A referrer log is a subset of the information a web-server records, each time a webpage is viewed. The referrer information records how users have linked to each file. With a little creative interpretation, referrer logs can provide information on:
If a webpage has no referring URI, the address may have been entered by hand or a user has clicked-through from an email. Referrer blocking software will also result in a empty referrer record.
In some hosting packages referrer logging is offered as an optional service.
Direct marketing campaigns often feature a unique URI that will redirect to a standard (i.e. not campaign-specific) product page. Tracking the number of times each unique URI is redirected to a standard webpage allows the campaign’s success to be measured.
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Internet security programs may be used to prevent a browser from sending referrer details. Blocking referrer details preserves the user’s privacy by not disclosing to a third party the other sites the user frequents. Although well-intentioned, this security feature has an unfortunate side-effect.
Ecommerce websites often use referrer details as part of the shopping basket system, e.g.:
If the referrer details are blocked, the processing page is unable to complete the redirection and the website may not perform as expected.
Referrer spam occurs when a program is used to create an artificial referrer record (on another site). It is
artificial as there is no true link from the referring URI to the website targeted.
Referrer spam capitalises on the practise of showing a referrer list on a webpage (including hyperlinks). If a referrer list is generated automatically from the referrer log, the spammer will indirectly generate links to their site without the consent of the site owner. As well as click-throughs, the induced incoming links may improve the search engine ranking of the spammer’s site.