This is more of a denial-of-service than a hack but Piergiorgio Zambrini discovered a way to crash the iPhone’s video player with what looks like an overflow error. The video file will simply put the iPhone into reboot mode and the hack works on OS X and Linux machines so it might be a Quicktime error rather than a full-on OS problem.
The hack can also take down iPods, depending on the model. Expect this to appear on your evening news tonight or tomorrow night with a breathless announcer intoning “Italian terrorists are after your iPhones? Find out more this hour on Fox 5 in Scranton.”