Looking at the Foreign Influence Taxonomy - 2018 (DHS) as a starting point to define this term, the scope is fairly broad:
This document also addresses "misinformation", "disinformation" and "malinformation".
Here are a few recent documents and webinars to provide some context around malign foreign influence:
And some reports and speeches on specific cases:
Covert, Coercive, and Corrupting: Countering the Chinese Communist Party’s Malign Influence in Free Societies
US efforts to counter Russian disinformation and malign influence