User interface mods are an important part of World of Warcraft. While over the years Blizzard has limited the functionality of its scripting language to prevent massive automation of tasks, mods are still seen as mandatory by the majority of the player base.
Apart from a few isolated incidents, most add-on authors congregate on two websites – Curse.com and WoWInterface.com. These sites provide not only a place for users to download the latest version of the mods, but also a centralised place for communication between authors and users. This has led to a situation where one or both of these sites have an effective monopoly on popular mods, with authors denying permission for add-ons to be hosted elsewhere.