UFO Video From Plane, Queensland Australia: 11/04/2012

A new UFO video sent in by a reader showing what looks like a huge black shadow ring, passing the aircraft.
Possibly a cloaked craft or even a black smoke ring? I would like your feedback on this footage:
I also want to remind everyone that this is one reason why I highly recommend when you fly to take a window seat, keep an eye on the skies outside and have your video cameras and smart phones