Plenty of script-driven apps, especially paid cms, encode their files to make sure that they won't be reverse engineered or tampered with. The majority of them use an app named ionCube PHP Encoder to do that, so, in case you acquire a paid script and you want to set it up in a hosting account, a software tool known as ionCube Loader needs to be present on the server. Without having it, you will not be able to install the script or if you somehow find a way to do this, it won't operate properly since most of the script code will be encoded to a degree where it can't be interpreted. That is why, you should ensure that ionCube Loader is present when you get a fresh web hosting account and you wish to work with some paid web application. If you buy a shared hosting account and the instrument is not present, it cannot be added since the whole server PHP environment shall have to be compiled again.