A lot of script-driven applications, especially paid cms, encode their files so as to ensure that they won't be reverse engineered or tampered with. Many of them use an app called ionCube PHP Encoder to do this, so, in case you acquire a paid script and you wish to set it up in a hosting account, a tool called ionCube Loader must be present on your server. Without it, you will not be able to install the script or if you somehow find a way to do this, it won't function efficiently because most of the script code will be encrypted to a point where it can't be interpreted. That's why, you should ensure that ionCube Loader is present if you get a fresh website hosting account and you would like to use some paid web application. If you acquire a shared web hosting account and the tool is not present, it cannot be added since your entire server PHP environment shall have to be compiled again.