Modern Warfare 3 Multiplayer is "Currently Unavailable?"

I started up Steam today to play some Modern Warfare 3, and finally play for more than 10 minute increments... Regardless the reason for me playing, the game would not start- and notified me:

"This game is currently unavailable. Please try again at another time."

My internet connection is working perfectly, as I am posting this question. Are the servers under maintenance, or have I somehow done something wrong?

This is actually a pretty common Steam issue. You might want to check out this help topic on the Steam support site.

I know this might be a bit late, but the other thing that worked for me was to just update modern warfare 3, it was 4.5mb and after that the game ran perfectly.