Activision tried to wash some of the egg off Infinity Ward's face when it announced that, in spite of all the protests and boycotts, Call of Duty Modern Warfare 2 outsold the original MW. But, all you PC gamers out there that feel frustrated that you can't sting your new “public enemy no.1” off the gaming scene learn that the developers had a few more things hidden from PC gamers. If you couldn't figure out why MW2 took so much hard-drive space, considering how short was the single-player campaign, then learn that at least some of that space is reserved for some hidden game mods.

These mods were first posted on the official IW forum, but have since then been removed. These are the modes along with their description, as they are hosted at modernwarfail2.com:
The first gametype - "gtnw" - is Global Thermonuclear War. To play, simply capture the objective: a nuclear bomb. When captured, the bomb detonates.
The second gametype - "oneflag" - is One Flag CTF. To play, capture the flag in the middle and bring it back to your base.
The third gametype - "vip" - is VIP. To play, defend the VIP. Or, if you're on the other team, kill the VIP.

These mods aren't really PC-exclusive, but, since they need the developer's console hack to enable them, Xbox 360 and PlayStation 3 users don't have access to them. What should be mentioned is that these modes have been as of this time only tested on the Afghan and Favela maps, so they may not work on other ones.

A lot of speculations have been flying around the community, and the general opinion is that these might be future DLCs for the game. There's no proof for this speculation at this point, but, most likely, these will never become a separate release from Infinity Ward anymore, even if they were part of the schedule. With these unveiled by the fan scene, if it did try to peddle this to gamers, it'd just confirm everyone's accusations. Another possibility is that these mods were not yet ready by the time of the game's release and that they're still under development. But if that was so, the developers could just admit it and not instantly delete every post made on the forum regarding these game mods. Right now, Activision has abstained from any public statements, but, if it breaks the silence, it will be a very interesting comment indeed.