1. Only gods have the ability to directly remove curses and similar magical afflictions. Without this aid, characters must have the curse properly identified (Read Magic would suffice). In any given cache of books being no less than one-hundred volumes, there is a base 5% chance that the Cureall Book will be present. The Cureall is an extensive and ancient collection of information and cures for all manner of hexes and magical diseases. With any given curse, there is a base 30% chance that no cure will be indicated. Typically cures consist of preparations involving time, lunar positions, sometimes rare material components, occasionally the presence of a living thing (or things) to absorb the curse when it is finally driven from the afflicted's body.
Addendum: Only certain monster types should be able to utilize curses, and only a set number of times per month or year. [A goblin tribe lucky enough to inherit a curse would covet its use.] As it is commonly practiced, a curse is used only when a situation seems to demand its use.
2. Hexes are the area-effect equivalent of curses. They alter an environment in ways that are usually not apparent until it is too late. There is a hex for poisoning wells, for bittering the flavor of hanging fruits, for causing rainclouds to accumulate over a home or copse of trees.
3. Magical Corruptions are effects that change the afflicted to his or her detriment. Consider Old King Cole's golden touch as a classic example. Some of the effects of items like Sauron's Ring or Stormbringer fall into this category.