I think it is Activisions Servers because CoD 4 is experiiencing the same issue, haven't tryed MW2 or W@W, but I know MW3 is still up and running.
Idk what is going on, maybe it has something to do with Hurricane Sandy and the power outages.
I dont know but i wish they would fix it. it's on defcon 4 right now, was on defcon 5 early this morning. wish they would hurry up there are a ton of us that want to play black ops. you can play campaign and a lan party but thats it.