Why didn't Dumbledore do anything about the attacks in Harry's second year?

In Harry's second year, when Muggleborns were attacked, why didn't Dumbledore set up security measure in Hogwarts right after Colin Creevey's attack to keep the rest of the Muggleborns safe? He could've asked the staff to implement rules like 'students are to be accompanied to each class by a teacher, quidditch is to be temporarily postponed', and such, right after Colin Creevy was petrified.