Debian Tutorials posted a guide about installing mod_spamhaus Apache module to fight comment spam on a Debian GNU/Linux based webserver

mod_spamhaus is an Apache module for DNS Block Listing that protects web services by denying access to particular IP addresses. It can stop spam relaying via web form URL injection, and block HTTP DDoS attacks from bot-nets.

It queries sbl-xbl.spamhaus.org, taking advantage of the Spamhaus Block List (SBL) and the Exploits Block List (XBL).

  Install mod_spamhaus Apache module to fight comment spam