A Malaysian Airlines 777-200 went missing over the South China Sea Saturday night. SAR crews have reported finding oil slicks but no flotsam from the missing airliner so far. Of note are reports of two stolen passports used to board the flight. Also noted is a repair to the wing of the aircraft made after a taxi collision back in 2009.
It appears at this early point that the aircraft may have been a casualty of terrorism or a catastrophic airframe failure perhaps stemming from the wingtip repair.
We're skeptical of the wingtip repair being a primary cause unless there was hidden damage in the structure of the wing which went unrepaired. A Japanese Airlines 747 crashed in 1985 due to structural failure from a previous repair to a pressure bulkhead so this is not unprecedented.
The other search avenue will be terrorism. Even if unauthorized people were on the aircraft, all airliners since 9/11 have been outfitted with armored doors which should be impervious to intruders. Had intruders been able to gain access to the cockpit presumably there would have been a struggle with the crew with the possibility of a distress radio call being made.
The other possibility is that a bomb was smuggled onto the aircraft. This would better explain the sudden disappearance of the aircraft with no distress calls but not necessarily the stolen passports unless the bomb was carried on in personal luggage.