A lot of licensed and some free of charge script-driven apps have encrypted code, that isn't human readable. The idea behind this is to stop the reverse engineering as well as the illegal usage of such applications. Among the most popular encryption tools used for this particular purpose is named Zend Guard and it's very popular as it can be used to change any PHP 4 or PHP 5 code. The only way for the encoded files to run correctly on a web server subsequently is if another instrument called Zend Optimizer is present. When you'd like to work with any paid web software that requires Zend Optimizer, you need to ensure that it is installed on the server where you will host your website. Also, websites that require the tool tend to perform better since their program code is already precompiled and optimized, meaning that it's executed more rapidly.