In the latest report, the diverted missing Malaysian Airlines plane was most likely programmed by someone in the plane's cockpit. This would require someone familiar with the Flight Management System in the plane, The New York Times reports.

From the Times:
Flight 370’s Flight Management System reported its status to the Acars, which in turn transmitted information back to a maintenance base, according to an American official. This shows that the reprogramming happened before the Acars stopped working. The Acars ceased to function about the same time that oral radio contact was lost and the airplane’s transponder also stopped, fueling suspicions that foul play was involved in the plane’s disappearance.
Whoever changed the plane's course had to be familiar with Boeing aircraft, and some officials said it was far-fetched to think that a passenger could have reprogrammed it.