Zend Optimizer is a popular software, that is needed to run files encrypted with Zend Guard. The latter encodes files written in PHP 4 and PHP 5 to protect them from reverse engineering and unauthorized usage, thus guarding copyright protected source code. When you would like to protect your custom-written script, for instance, you're able to employ Zend Guard and your code will not be human readable, but you'll also need Zend Optimizer on the server where you host your site. Various ready-made script-driven apps, especially ones that are paid, also need Zend Optimizer so as to function effectively because their core code is often not free to change. Internet sites which use the tool are normally faster since their program code is already optimized and precompiled.