Modern Warfare 2 - Multiplayer Perks are upgradable

Infinity Ward's Fourzerotwo discusses the tweaks made to Modern Warfare 2's multiplayer, including upgradable Perks; allowing players to "rank up" their Perks to an "upgraded Pro version.

Perks are subtle modifiers used within Modern Warfare and World at War's multiplayer that allow players to customise their play style, and gain access to a handful of advantages.

"We've made extensive additions to the perk system and create a class system as a whole. You can now customize killstreak rewards in addition to your weapon loadout, so your reward for multiple kills without a death can be customized to how you like to play.

This new addition along with the ability to rank up Perks from their base benefit to an upgraded Pro version with additional bonuses allows you to really customize your Classes to your preferred play style per gametype."

New Perks are unlocked as players reach new ranks, and those included in the original Modern Warfare include the Bandolier Perk for extra ammunition, or Sleight of Hand, which allows for faster reloading.