I was just reading a report on CNN that states that MAL 'DOES NOT' subscribe to the ACARS aircraft monitoring so no data was uploaded during the 4 hour period. But it did also say that even if the airline does not subscribe to the ACAR's Satcom service the aircraft will still ping the satellites and establish contact because that is how the 777 system is designed, the fact that MAS doesn't subscribe does not effect that. It is these 'pings' that they have now found to have carried on for 4 hours after last contact and they apparently will only happen whilst the aircraft is powered with engines running. The report also said that the aircraft could be airborne on land or indeed just flying around in circles.