Block Referer Spam for WordPress

Block Referer Spam stops the bots that fake an HTTP_REFERER header to advertise their own site in your traffic logs and analytics. They’re good enough at simulating real visits that they show up in Google Analytics right alongside genuine traffic — this plugin blocks the known offenders before they’re ever logged, and needs no configuration to start working.

Two blocking modes cover different hosting setups:

Rewrite mode (Apache only) — adds RewriteCond rules to .htaccess so spam requests are rejected by the web server itself, before WordPress even loads. Fastest option, and the default when your host is detected as Apache.

WordPress mode — checks the referer during normal WordPress request handling and returns a 403. Works on any host, including nginx, but can’t intercept a request that’s served entirely from a full-page cache (see the FAQ below) — the plugin will warn you on its settings page if it detects an active caching plugin while running in this mode.

The block list itself is a mix of several public spam-referer sources, merged and refreshed automatically once a day (or on demand from the settings page). You can also add your own domains to block, including internationalized (non-ASCII) domain names — they’re normalized automatically.

From Wikipedia:

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 benefits the spammer because the free link improves the spammer site's search engine ranking owing to link-counting algorithms that search engines use.