"leak" might be used to denote the release in a more passive / accidental sense, whereas "breach" in its traditional usage denotes a purposeful attack, such as

"leak" might be used to denote the release in a more passive / accidental sense, whereas "breach" in its traditional usage denotes a purposeful attack, such as if the release stemmed from a wilful actor. From the Oxford English Dictionary: Breach. A gap in a wall, barrier, or defence, especially one made by an attacking army.