How do we know for sure that ISIS has such missiles and that they did it?There's more to it then that. BA was specifically warned 3 months ago not to fly too low over Sinai because of ISIS:
http://www.dailymail.co.uk/news/art...-ago-fears-anti-aircraft-missile-attacks.html
The question then becomes how does ISIS get hold of missiles that can reach 25,000 ft