In contrast to Blood Magic, Corruption magic is about subtle changes. Though Corruption spells may indeed have obvious visible effects at times, the havok they wreak is of a nuanced sort. Through intense study, Necromancers have found that Corruption need not always be detrimental, that they can invoke corruptive effects on themselves that aid them in their work. Often the misconception is that Corruption magic must work against the mind, whereas Blood Magic must instead attack the body, but those fools later find out to their great dismay that this need not be the case. Corruption magic has proven adept at the creation of diseases or pathogens. While the cities and governments still abhor the use of Corruption magic, some of it is difficult to detect and none of it is frowned upon in any active way by the divinities themselves.
In short, Corruption deals with the conjuration of poison, disease, and more refined forms of illness.
Corruption is the second "pure" spellbook, analogous to the former Corruption Necromancy book. It deals exclusively with the results of mixing Life and Lunar mana.
This mana mixture works through decay of various forms, from flesh-eating bacteria to diseases of the mind. Corruption includes many of the Necromancers' most subtle spells, some of which are "legal" by dint of the fact that no one around the Necromancer can detect anything wrong has happened.
Conjured poison and disease falls under this category, as well as obscure forces that corrupt the emotional balance and mental faculties of the target. Some of the effects of Corruption could be poetically said to cause a "soul sickness," but these spells cannot actually impact the health of the victim's spirit.