Using .htaccess to block referrer spam

Lately referrer spam became a great annoyance for the webmasters. If you are not sure what referrer spam is you may wish to check this article: http://en.wikipedia.org/wiki/Referrer_spam

To block these spam referrers you need the following lines in your .htaccess file:
# set the spam_ref variable
SetEnvIfNoCase Referer "^http://(www.)?some-spammer.com" spam_ref=1

SetEnvIfNoCase Referer "^http://(www.)?other-spammer.com" spam_ref=1

SetEnvIfNoCase Referer "^casino-poker" spam_ref=1

# block all referres that have spam_ref set
<FilesMatch "(.*)">
Order Allow,Deny
Allow…