No where near 6.5 million copies sold on steam
the sales figures quoted are for all formats, just shy of 200,000 copies where sold in the first week on PC , that number pretty much fell off instantly. on average there are less than 20k playing at any one time, a little more due to this free weekend but the game still sufferes from console-port-itus. horrible p2p lag infested listenservers with huge penalties for those with fast PC's and internet connections in the way of added fake lag compensation. It truely is a mere shadow of what was one a great PC franchise.
Added to this the fact that hacks and cheats are freely availible all over torrent sites etc, hacks that have been around since MW2 over 2 years ago and still not addressed by the developer and all in all its a horrid experience.