You can read more about it here: viewtopic.php?f=22&t=2268Drakath wrote: There has been a lot of work on the stealth mechanics. We have noticed that not many players were interested in this feature and thus it has been made easier and more fun to use.
Zombies in un-alerted zones will no longer detect players who are not in their field of view. The field of view is lower if you are crouched.
In addition to hearing bullet and explosion sounds, zombies will now take into account the sound of your movement.
Sprinting makes the most noise, jogging makes a bit less, walking makes very little and moving while crouching makes virtually no noise.