This is a simple glitch used to acquire all the perks at a low level. It works about 75% of the time, If not, try again when you reach another perk level (Look below for details.)

Requirements:

* Must be in between levels for unlocking a perk. Ex: Level 16, and 17, Unlocking Scrambler at 17.
* Wired connection, Wireless won't work.

Steps:

For this tutorial, I will be using the Scrambler perk as an example here.


* Step 1: Be a level 16, and almost rank up before you enter any game.

* Step 2: Search for any game, and once you find one, rank up in it to unlock Scrambler.

* Step 3: Once you've ranked up in the game wait until the game is over.

* Step 4: When the scores show up on your screen and after the game is over, and you are back in the lobby ( DO NOT PRESS ANY BUTTONS ) and quickly unplug your ethernet cable.

* Step 5: Then reconnect it, and connect to Xbox Live. Every perk after Scrambler is now unlocked.
From:http://www.se7ensins.com/forums/modern-warfare-2-glitches/168310-unlock-all-perks-earlier.html
Fro