1-) Go in a lobby and make sure YOU ARE THE HOST; (You can test with a friend on a private match)
2-) Attach Cheat Engine to MW3, kill someone, put 1 on the filed Value on CE an click New Scan;
3-) Kill someone again, and put 2 on CE and click Next can. Repeat this changing the numbers for the number of kills you have, if you die, put 0 and click Next Scan;
4-) If you did everything right, when you get 4 or 5 kills you will have some addresses on CE that start with 020..... Select all this addresses and move them to the table(Click the Red Arrow);
5-) Select all the Addresses on the table, right click and go in "Change Record -> Value" put 24, or 23(If you have hardline).
6-) Click on the box that says "Active" to freeze the addresses and it's done. For each kill you'll get a moab.
I'm not good at explaining things, but I can make a video if you still want.
But remember, This is Dangerous and might cause you a Ban, specially if other player report you. I don't believe that VAC scans for memory writing unless you have been reported, cause.. well, I'm not banned and I have been writing/reading memory since last month. But still, Use at Your Own Risk