What is most puzzling is the manner in which the aircraft disappeared. Not mayday call or anything. Even if the engines stopped turning there's batteries and ram air turbines to provide power for communications etc to get a call out.
So it's leading to speculation that the aircraft broke up at cruise altitude and other than acts of terrorism I don't think that's been an issue for many years.
It's still very early for speculation like that. Air France 447 in 2009 was similar to begin with, just "disappearing" over water. It turned out there were some automated messages sent, but that was not reported for several days.