Infect 1000 players in DarkOps: Infection. The quickest way to get this achievement, is to set up a match with the following settings:
Map: Old Town
Map Size: Small
Points Limit: None
Round Limit: 10
Time Limit 3
Starting Money: 15,000CR
Weapons: Disallow all except Multi-Mines and the SuperDragon.
If you start as the infected (skeletons), you must kill the humans. Each kill against a human is one infection. As you start with only a pistol when infected, it is a good idea to press to put your gun away, then when you're near an enemy. This will allow you to steal their weapon.
When you begin the round on the humans side, buy the SuperDragon and Multi-Mines. Again, you want to kill the humans (teamkill). Do not under any circumstances suicide when you are a human, as you will need to sit out the rest of the round. If you're killed as a human, you will be turned to the infected side. Using this method you can get between 300-400 kills each hour. Therefore, it will take two and a half to three hours to infect 1000 players. It can be a mix of online and offline.
*You must complete the match for your achievement progress to register.