Modern Warfare 2 features new Perks and retains some older ones from Call of Duty 4. Each Perk can now be upgraded to a "Pro" version, by completing its challenge.
Note: the upgrades don't always make the Perk stronger, instead it might add a new feature or a side effect, e.g: Marathon Pro allows you to get over obstacles faster.
Below is the list of current known Perks.
Akimbo | Akimbo Pro
Ability: Allows to dual-wield any sidearm.
Pro Ability: ?
Note: Akimbo is confirmed, but its Perk Slot is unknown (slot 1, 2 or 3)
Perk Slot 1
Marathon | Marathon Pro
Ability: Unlimited sprint.
Pro Ability: Get over obstacles faster.
Sleight of Hand | Sleight of Hand Pro
Ability: Faster reloading.
Pro Ability: ?
Scavenger | Scavenger Pro
Ability: Full resupply from dead enemies.
Pro Ability: ?
Bling | Bling Pro
Ability: 2 primary weapon attachments.
Pro Ability: ?
Classified (needs to be unlocked)
Ability: ?
Pro Ability: ?
Perk Slot 2
Stopping Power | Stopping Power Pro
Ability: Increased bullet damage.
Pro Ability: Increased bullet damage vs. vehicles.
Lightweight | Lightweight Pro
Ability: Move faster.
Pro Ability: ?
Hardline | Hardline Pro
Ability: Killstreaks require 1 less kill.
Pro Ability: ?
Cold-Blooded | Cold-Blooded Pro
Ability: Undetectable by UAV, air support, sentries, and thermal.
Pro Ability: ?
Classified (needs to be unlocked)
Ability: ?
Pro Ability: ?
Perk Slot 3
Commando | Commando Pro
Ability: Increased melee distance.
Pro Ability: ?
Steady Aim | Steady Aim Pro
Ability: Increased hip-fire accuracy.
Pro Ability: ?
Scrambler | Scrambler Pro
Ability: Scrambles (jams) the enemy radar in a small radius.
Pro Ability: ?
