Soul corruption is something that can happen to anybody who uses with magic and does Spell Weaving. Soul corruption is a negative effect on the caster if they stack more spells than they can handle when weaving. The actual amount of spells you can weave into one spell is dependent on your level and is never an exact science. The effect from Soul Corruption can vary, up to even killing the caster.
There are methods to lessen the amount of Corruption that a player has, exact details of this and what is needed is not yet known, nor how quickly someone builds up Soul Corruption.