Many licensed and some cost-free script-driven apps have encrypted code, which is not human readable. The idea behind this is to prevent the reverse engineering as well as the unwanted usage of such apps. One of the most popular encryption software tools used for this specific purpose is known as Zend Guard and it is used widely as it can be used to alter any PHP 4 or PHP 5 code. The sole way for the protected files to run effectively on a web server subsequently is when another instrument called Zend Optimizer is present. If you wish to use any paid web software that needs Zend Optimizer, you have to make sure that it is set up on the server where you will host your site. Also, websites that require the tool can perform better as their code is already precompiled and optimized, which means that it's executed more rapidly.