using System;

using System.Collections.Generic;

using System.Text.RegularExpressions;

using System.Threading.Tasks;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var cc = new List<string>()

        {

            { "378282246310005"},

            { "371449635398431"},

            { "378734493671000"},

            { "5610591081018250"},

            { "30569309025904"},

            { "38520000023237"},

            { "6011111111111117"},

            { "6011000990139424"},

            { "3530111333300000"},

            { "3566002020360505"},

            { "5555555555554444"},

            { "5105105105105100"},

            { "4111111111111111"},

            { "4012888888881881"},

            { "4222222222222"},

            { "5019717010103742"},

            { "6331101999990016"},

            //Hyphens

            { "3782-822463-10005"},

            { "3714-496353-98431"},

            { "3787-344936-71000"},

            { "5610-5910-8101-8250"},

            { "3056-930902-5904"},

            { "3852-000002-3237"},

            { "6011-1111-1111-1117"},

            { "6011-0009-9013-9424"},

            { "3530-1113-3330-0000"},

            { "3566-0020-2036-0505"},

            { "5555-5555-5555-4444"},

            { "5105-1051-0510-5100"},

            { "4111-1111-1111-1111"},

            { "4012-8888-8888-1881"},

            { "4222-2222-22222"},

            { "5019-7170-1010-3742"},

            { "6331-1019-9999-0016"},

            //as part of a sentence

            { "my number is3782-822463-10005"},

            { "hi my number is 3714-496353-98431"},

            { "3787-344936-71000 is my number"},

            { "5610-5910-8101-8250is my number"},

            //spaces

            { "3782 822463  10005"},

            { "3714 496353  98431"},

            { "3787 344936  71000"}

        };

        var reg = new Regex(@"(?<=\d{4}\d{2})\d{2}\d{4}(?=\d{4})|(?<=\d{4}( |-)\d{2})\d{2}\1\d{4}(?=\1\d{4})");

        cc.ForEach(x => Console.WriteLine(reg.Replace(x, new MatchEvaluator((m) => new String('*', m.Length)))));

    }

}