Malfeasance is the harmful use of sympathy or arcane knowledge against another.
Malfeasence is widely considered forbidden among Arcanist's and rarely occurs in the current time period of The Four Corners of Civilization. A student of the Arcanum who is convicted of malfeasence faces expulsion and possible whipping. What happens to a full Arcanist convicted of the crime is often decided by the ruling Lord. Most likely however, a Full Arcanist found guilty of Malfeasence would face a death sentence.
Malfeasence is most easily done through the use of sympathy, requiring a small amount of the targets blood or hair as well as a likeness of them called a mommet.
In The Chronicle
During Kvothe's second sympathy class at The University, Master Hemme challenges his knowledge of the subject by arrogantly allowing him to teach the class. It becomes clear however that Master Hemme has underestimated Kvothe's skill and ability when he is given a sympathetic "hot foot" by the student. Afterward, Master Hemme accuses Kvothe of malfeasence, a charge that is later reduced after the events of the account unfold. Ultimately, Kvothe's use of a double binding and subsequent blistering of the Master's foot earns him promotion to the Arcanum at the title of E'lir.
Also in the Chronicle, Kvothe becomes the unwitting victim of malfeasence conducted by Ambrose Jakis after Kvothe breaks into his room and leaves behind some of his blood. This leads to Kvothe's struggle to construct a Gram which would protect him from the attacks. However, he is forced to battle Ambrose's alar until the advanced schema for the artifact can be acquired. His friends Simmon and Wilem assist him, warding his body with their own alar's while Kvothe sleeps. Due to their careful conduct during this part of the story, Kvothe is never definitively proven to be the burglar.
When Kvothe travels to Severen to meet and work with Maer Alveron, he discovers that the Maer is the subject of a different sort of malfeasance involving Alchemy. It is revealed that the Maer's sickly condition when Kvothe first met him is due to his systematic poisoning at the hands of his personal arcanist, Caudicus.