Taken directly from the manual (http://www.planetunreal.com/infiltration/manual), (specifically here (http://www.planetunreal.com/infiltration/manual/controls.htm#score)):
SCORE:
The way scoring is handled in Infiltration is simple. One point is awarded for every 20 healthpoints subtracted from the enemy. Five additional points are awarded for every kill. Finally, five more points are awarded for all survivors of a round. In the future when bleeding and bandaging is in place, this style will be altered and the manual updated in kind.
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I make dead people.