Date: 07/24/06 (Java Web)    Keywords: spam

You can easily and effectively use your .htaccess file to easily and effectively block comment and referrer spammers targeting your blog(s). If you are using WordPress you can also use my Referrer Bouncer plugin, which is much simpler, to block referrer spammers. For the rest here is a sample .htaccess file you can start with. # [...]

Source: http://blog.taragana.com/index.php/archive/simple-htaccess-rules-to-block-spammers/