This article shows how to install and configure ModSecurity (version 2) for use with Apache2 on a Debian Etch system. ModSecurity is an Apache module that provides intrusion detection and prevention for web applications.
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In Debian Sarge, ModSecurity was available as a .deb package in the official Debian repositories, but in Debian Etch it was removed due to some license issues. Fortunately, the original maintainer provides packages for Debian Etch in his own repository.