spread of terrorism

The father of an American woman killed in the Paris terrorist attacks sued Twitter, Facebook, and YouTube,alleging the sites knowingly allowed ISIS terrorists to recruit members, raise money, and spread extremistpropaganda. The sites defended themselves by saying that their policies prohibit terrorist recruitment and that,when alerted to it, they quickly remove oending videos. What type of lawsuit is this—criminal or civil? Whatresponsibilities, if any, should social media sites have for the spread of terrorism?