mod_defensible is an Apache 2.x module intended to block spammers/hackers/script kiddies using DNSBL servers. It will look at the client IP and check it in one or several DNSBL servers and return a 403 Forbidden page to the client. This guide shows how to install and use it with Apache 2 on a Debian Etch server.
Read it at howtoforge
Unfortunately libapache2-mod-defensible is available as a Debian package only for Debian Lenny (testing) and Sid (unstable), but not for Etch. Therefore we will install the libapache2-mod-defensible package from Lenny. To do this, open /etc/apt/sources.list and add the line deb http://ftp2.de.debian.org/debian/ lenny main; your /etc/apt/sources.list could then look like this: