Suhosin is an advanced protection system for PHP installations.
It was designed to protect servers and users from known and
unknown flaws in PHP applications and the PHP core.
Suhosin comes in two independent parts, that can be used
separately or in combination. The first part is a small patch
against the PHP core, that implements a few low-level
protections against bufferoverflows or format string
vulnerabilities and the second part is a powerful PHP extension
that implements all the other protections.

Suhosin is binary compatible to normal PHP installation,
which means it is compatible to 3rd party binary extension
like ZendOptimizer.

WWW: http://www.suhosin.org/