Zend Optimizer is a well-known software, that's needed to execute files encoded with Zend Guard. The second encodes files written in PHP 4 and PHP 5 to protect them from reverse engineering and not authorized use, thus guarding copyrighted source code. If you want to protect your custom script, for instance, you'll be able to use Zend Guard and your code won't be human readable, but you'll also need Zend Optimizer on the server where you host your website. Numerous pre-made script-driven apps, particularly ones which are paid, also require Zend Optimizer in order to operate properly since their core code is often not free to change. Sites that use the instrument are normally faster because their code is already optimized and precompiled.