I played a little bit around with the Scoring for Civilians on Terrormissions.
Each killed Civilian now gives 50 Points towards the aliens instead of 30.
The screenshot is from a Debugtest, were all Civilians got turned into Zombies and all aliens were killed after that.
Each Zombified Civilians count double towards the score.
Nevertheless you will never encounter such a scenario, since many Civilians will just be killed by other means then zombification.
Even thou it is pretty impressive