Just a warning for everyone it looks like the hackers of MW3 were able to mod a vault file and have been passing it around to all their friends. If you are asked to view any vault video entitled "FAIL!" do not watch it. It will reset your rank to level 1 no prestige.
Anyone who also lurks on the callofduty.com/mw3 forums may have seen a thread about this. Hopefully it will be patched soon. But just a heads up for everyone! Stay safe and avoide vault videos for a while! Enjoy the double xp weekend.