$(document).ready(function(){
  $("#contactform").validate({
    rules: {
      sc: {
        required: true
      },
      spamtest: {
        required: true,
        equalTo: "#sc"
      }
    },
    messages: {
      spamtest: {
        required: "This is required to avoid spam posts from the internet.",
        equalTo: "The entry must be BRUTE!"
      }
    }
  });
});