Learn English – word/adverb that describes that “something was done which shouldn’t have been done”

Is there a word for "something was done which shouldn't have been done" in the English language?

For example, let's say a soldier fires a shot even though his commander ordered a cease fire, you could say:
"The soldier erroneously/fallaciously fired a shot, despite the order of his superior officer."

Is there a better word for erroneously/fallaciously in this context?
Something that places more emphasis on the fact that it was an action that was performed by the subject which [under general consensus] was explicitly advised against or even prohibited to be performed by the subject.

Erroneously/fallaciously places more emphasis on that it was "wrong", but I'm looking for something else here…