With Halo 4 now available worldwide, Microsoft is holding a limited-time only promotion where you will get free Microsoft points, by simply putting playing multiplayer for a number of hours.
Starting today through the rest of November, every hour that you spend the multiplayer portion of Halo 4 will be counted towards the amount of points you can get. Let say you spend 70 hours from now till November, well at the end, you will receive 300 Microsoft Points. If you want more than that, you can get 600 Microsoft Points for playing 140 hours!
If racking up some free points sounds good to you, make sure that you are signed up on their Xbox Live Rewards program. Head over to this page for more information.