The ban itself isn't relevant to it supposed goal.
Between 1975 through 2015, 17 foreign-born folks from these nations were convicted of carrying out or attempting to carry out a terrorist attack on U.S. soil and they killed zero people. Zero Libyans or Syrians intended to carry out an attack on U.S. soil during this time.[1]
None of the post-9/11 terrorists in the United States came from any of the targeted countries (and none were refugees) either. Both the 9/11 terrorists and the few non-domestic Muslim post-9/11 terrorists that actually carried out attacks were non-refugees from countries not covered by the order.