Lots of script-driven apps, particularly paid cms, encrypt their files to ensure that they won't be reverse engineered or tampered with. Most of them use an app called ionCube PHP Encoder to do this, so, in case you get a paid script and you intend to set it up in a website hosting account, an instrument known as ionCube Loader needs to be present on your server. Without it, you can't install the script or in case you somehow find a way to do this, it will not function effectively for the reason that most of the script code will be encrypted to a point where it cannot be interpreted. That is why, you should ensure that ionCube Loader is present if you get a new hosting account and you want to use some paid web application. If you purchase a shared web hosting account and the instrument is not present, it cannot be added because the whole server PHP environment shall have to be compiled again.