Numerous licensed and some free of cost script-driven apps have protected program code, that is not human readable. The concept behind this is to avoid the reverse engineering as well as the unwanted usage of such applications. Among the most popular file encryption tools used for this specific purpose is named Zend Guard and it is very popular due to the fact that it can be used to alter any PHP 4 or PHP 5 code. The only method for the encoded files to work the right way on a web server afterwards is if a second tool called Zend Optimizer is there. When you'd like to work with any kind of paid web software requiring Zend Optimizer, you need to ensure that it is set up on the server where you'll host your website. In addition, websites that need the tool will perform better as their program code is already precompiled and optimized, meaning that it's executed quicker.