Lots of licensed and some cost-free script-driven applications have encrypted program code, that is not human readable. The concept behind this is to avoid the reverse engineering and the unwanted usage of such applications. One of the most popular file encryption instruments used for this specific purpose is called Zend Guard and it is very popular since it can be used to modify all PHP 4 or PHP 5 code. The only way for the protected files to work the right way on a web server after that is when an additional instrument called Zend Optimizer is present. In case you would like to work with any kind of paid web software that requires Zend Optimizer, you need to ensure that it's set up on the server where you will host your site. Furthermore, sites that require the tool tend to perform better since their program code is already precompiled and optimized, and therefore it is executed quicker.