Doing something which is illegal.
In Proksch v. Bettendorf, 218 Iowa 1376 (1934), the Supreme Court of Iowa adopted these words:
"Nonfeasance ... means the omission of an act which a person ought to do.
"Misfeasance is the improper doing of an act which a person might lawfully do.
"Malfeasance is the doing of an act which a person ought not to do at all."