malfeasance is "evil doing"; the commission of an act which is positively unlawful and wrong.

misfeasance is the improper performance of some otherwise lawful act.

nonfeasance is the omission of an act which a person ought to do.

To quote from Desmarais v Wachusett Regional School District, 360 Mass 519; 276 NE2d 691:

There is a distinction between "nonfeasance" and "misfeasance" or "malfeasance"; and this distinction is often of great importance in determining an agent's liability to third persons. "Nonfeasance" means the total omission or failure of an agent to enter upon the performance of some distrinct duty or undertaking which he has agreed with his principal to do; "misfeasance" means the improper doing of an act which the agent might lawfully do, or, in other words, it is the performing of his duty to his principal insuch a manner as to infringe upon the rights and privileges of third persons; and "malfeasance" is a doing of an act which he ought not to do at all.