Spell Risk is the chance that use of the spell will be detected, typically in an area where "a great evil" is actively searching for such use (or at least for intruders). Roll 100OE + the risk factor, on 100+ something has been detected. That could result in nothing, active search in the area for the caster, search for the caster and they know the exact location at the time of casting, a creature, patrol, assassin, or army unit in the area begins hunting the caster, etc. The risk factor is highest for elemental spells and lowest for information spells; the risk factor also depends on the level of activity of the evil forces. Ranging from -25 chance for an information spell in a low activity area to +75 for an elemental ball spell in a very high activity area.
Corruption represents the chance that the character is corrupted by darkness. Optionally you can make a corruption roll for every spell failure. Again, elemental spells are the most dangerous and information spells the least so. The caster also gets an RR to only take half the corruption points. Corruption points are not awarded if the spell was appropriate for "pure" goals. Massive overkill is not "appropriate"! You might also take corruption points from evil items, etc.
When tempted by evil, the character rolls 100OE-3xSD+Corruption points. 100+ means the character will give in. In the presence of an "evil being" the character must make an Essence RR +3xSD -CP. On failure, they must obey.
These are meant as optional rules to control the use of magic. The risk factors make sense when the characters are sneaking through a heavily patrolled area, but you wouldn't use them just generally wandering through the countryside (unless you have a very dark campaign). Corruption implies that there is something dark and malicious behind magic (or you might only apply it to certain kinds of magic), e.g. the magic you are using is demonic in nature.