As Infected was implemented into the community playlist on Modern Warfare 3 and drop zone was taken out, I have a simple tip that will have you not getting infected online. This tip only works on certain maps, however it could be crucial.

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Instructions

1. Whatever map you are playing, make sure you have a brief knowledge on things that you climb up (e.g. ladders)

2. When the countdown starts, run to the nearest ladder and stay on it.

3. Once the countdown reaches zero, you will not be chosen as an infected.

4. Play as a survivor until you get killed by an Infected.

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This works on any maps with ladders, just as long as you can get there before the timer gets you. This is somewhat a glitch you could say but it's definitely fun to pull off, especially in a private match and amaze your friends.