The online multiplayer mode of Modern Warfare 2 retains the same experience points and unlockable reward system as that of Call of Duty 4, with game modes that include Free-For-All, Search & Destroy, Demolition, Sabotage, Domination, Team Deathmatch, and Capture The Flag. Modern Warfare 2 introduces several new features. Aside from new weapons, equipment, and perks that upgrade to “pro versions” after meeting utilization requirements, the player can choose three of fifteen killstreaks, which are earned after getting a certain amount of consecutive kills. Among these is the ability to receive a supply drop after achieving four kills in a row, guide a Predator missile strike after five kills, and control an AC-130 gunship, or Chopper Gunner, after eleven kills. Some killstreak rewards earn kills that go towards your killstreak. For example, Harrier Strike (7 killstreak) will stay and shoot down enemies after it has bombed a general area. Players can also gain a tactical nuke if they obtain a 25 kill streak. The nuke will achieve victory in a match for the player or team that called in the nuke regardless of whether the team was winning or losing at the time the nuke was called in. Another new feature is the in-game host migration; if a match host leaves the game, or if the host struggles to support the game, a ‘host migration delay’ allows a new host to be selected and the game to continue. There is also the addition of an optional third person mode which can be used in certain game types.
For the PC version, Infinity Ward decided to implement a new matchmaking service called IWNET, which works through Steam. This system is nearly identical to the console version of IWNET. Dedicated server support is removed, eliminating the ability for mods or user-created maps to be incorporated. This removal has created anger among many PC gamers. Since the multiplayer aspect runs within Steamworks, the PunkBuster anti-cheat system utilized in previous titles has been replaced by Valve Anti-Cheat. In addition, the PC version shares the same 18-player cap as the console versions (matches are a maximum of 9 versus 9).