Plenty of licensed and some free of cost script-driven apps have encoded program code, which is not human readable. The idea behind this is to avoid the reverse engineering as well as the unauthorized usage of such applications. Among the most popular encryption software tools used for this specific purpose is named Zend Guard and it's widespread due to the fact that it can be used to change all PHP 4 or PHP 5 code. The only way for the encrypted files to work efficiently on a web server subsequently is when a second tool called Zend Optimizer is there. In case you'd like to work with any type of paid web software requiring Zend Optimizer, you have to make sure that it is set up on the server where you'll host your site. In addition, websites that require the tool generally perform better due to the fact that their program code is already precompiled and optimized, and therefore it is executed more quickly.