I was working for Emirates . Operating Heathrow to Dubai and some where over Iran when we became aware of an issue. Company ACARS to stop cockpit access and pilot chatter on 123.45 that numerous more aircraft had possible terrorists on board. Nothing from ATC or formal channels. Years later I was inbound to Istanbul when a terrorist attack was underway and was alerted by cabin crew who had been informed by passengers watching BBC world on inflight entertainment.