The governing body of Formula 1, the FIA, can award one of two penalties to a driver a driver who overtakes under yellow flag conditions. If awarded during a race the driver will receive a drive through penalty. If awarded after the race the penalty is a 20 second addition to the drivers race time.
If the FIA penalise Sebastian Vettel with a 20 second penalty to be added to his race time then Fernando Alonso, rather than Vettel, will be the 2012 F1 World Champion.
This video clearly shows that Vettel did overtake under a yellow flag. Ferrari are planning to protest. Watch this space, things could be about to get messy.
(note - as fast as the FIA withdraw videos of this incident - which they are doing - from youtube we find another to use. Please let us know if this version doesn't work)