using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string input = "<a href=\"javascript:alert(1)\">abc</a>";

        string output = Test(input);

        Console.WriteLine(output);

    }

​

    public static string Test(string input)

    {

    return Regex.Replace(input, "(<a\\s(\\s*(target=\"blank\")\\s*(href=\"((https{0,1}://){0,1}[A-Za-z0-9#\\./_\\s\\-:()-çığöşüÇİÖĞÜ]+(\\?([A-Za-z0-9_]+=[A-Za-z0-9_]+&{0,1})*)*\"))\\s*)\\s*(target=\"_blank\")*\\s*(onclick=\"window.open.'((https{0,1}://){0,1}[A-Za-z0-9\\./_\\s\\-:]+(\\?([A-Za-z0-9_]+=[A-Za-z0-9_]+&{0,1})*)*)','ExternalPage'.;return false;\")*\\s*>)", "", RegexOptions.None);

​

    }

}