I have seen a couple things on Twitter tonight that some people have started hacking Modern Warfare 2 on the PC. I will keep this post updated when I continue to find more things. For now, this is what I have. I would suggest staying off of the PC version tonight.
Level Down: http://bit.ly/5nz1WK
Level Up:
Level Down: http://www.youtube.com/watch?v=wrhueUVKufY