"Honeywell is debunking fears about bogus CPDLC messages, sparked by an event last month involving a Gulfstream G550 flying in Shanwick Ocean Control airspace over the northeastern Atlantic Ocean. According to a Flight Service Bureau blog post, the G550 crew received a “DESCEND AT MAXIMUM” message via CPDLC, but when they checked on voice with ATC, it hadn’t come from them.
But Honeywell said the “↓ DESCEND AT * MAXIMUM” message was actually a downlink message to ATC from the FMS (as indicated by the down arrow), not an uplink from ATC."
Honeywell Debunks Reports of Bogus CPDLC Messages | Business Aviation News: Aviation International News