Block Spammers/Hackers With mod_defensible On Apache2

mod_defensible is an Apache 2.x module intended to block spammers 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.

Installation
Download the package: here

Follow the steps below to compile and install the package.

# tar -zxvf mod_defensible-1.4.tar.gz
# cd mod_defensible-1.4/
# ./configure
# make
# make install

You can use --with-udns to enable udns (asynchronous resolver library) usage, which should be faster. However, this is not mandatory.

Configuration
Open (apache configuration file) apache2.conf and go to the end where the virtual hosts are configured, and put the mod_defensible configuration right before the virtual hosts:

# Activate DNSBL usage
DnsblUse On
# Specify DNSBL servers
DnsblServers xbl-bl.spamhaus.org. mydnbl.server.org.

With udns support, you can also use:

# Specify another nameserver to use instead of default system resolver
DnsblNameserver 192.168.3.254

Restart Apache afterwards: /etc/init.d/apache2 restart

That's it. If an IP address which is blacklisted tries to access your webserver, it will receive an HTTP error 403.