Malaysian Airlines Bombing?

Reports that two people (now four) were flying using stolen European passports. Were these western-looking suicide bombers that wanted to kill a lot of Chinese? I suppose it's possible, but it doesn't quite add up. Are the separatists in Western China responsible?

Update: Now the speculation is that it was a hijack attempt, possibly that the four suspicious passengers took over the cockpit before the jet crashed. The wreckage seems to be in the South China Sea, off the coast of Vietnam.