using System;

using System.Linq; 

using System.Collections.Generic;

using System.Text.RegularExpressions; 

public class Program

{

    public static void Main()

    {

        List<string> lista = new List<string>();

        lista.Add("ABC;");

        lista.Add("123;");

        lista.Add("\"XYZ\";");

        lista.Add("\"A B; C\";");

        lista.Add("\"Uma string" + '\n'.ToString() +

        "com ; várias" + '\n'.ToString() +

        "linhas;\";");

        foreach(var input in lista) {

            foreach (Match match in Regex.Matches(input, "(?!.*\");", RegexOptions.Singleline)) {

                Console.WriteLine("-----------------");

                Console.WriteLine("{0} - '{1}' encontrado com index {2}.", input, match.Value, match.Index);

                Console.WriteLine("-----------------");

            }

        }

    }

}