On March 1, 2020, a pro-Islamic State (ISIS) group put out a poster claiming that "kuffar spies" have a back door to the Elliptic Curve Diffie–Hellman (ECDH) encryption used in the Blockchain Messenger (BCM) app, further advising ISIS supporters to delete BCM from their devices.
Source: Rocket.Chat, March 1, 2020.