C# simple class to convert a URL into acceptable windows file name

Hi, i was working on a project that takes screen-shots of web pages that are loaded in to Internet Explorer browser.As per the clients requirement, I need to save the screen-shot of a web page using the later ‘s URL.
I searched the web to find some help, but found nothing that matches my criteria, then i decided it do it my own way, write your own class file for converting a URL into an acceptable windows filename.
here is the code that will change a URL into a filename.

using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

namespace Coderbuddy
{
public class FileNameFromURL
{
string URL = "";
public FileNameFromURL(string URL2CONVERT)
{
URL = URL2CONVERT;
}

public string CONVERT()
{
List<string> X = new List<string>();
string rt = "";
Regex r = new Regex(@"[a-z]+", RegexOptions.IgnoreCase);
foreach (Match m in r.Matches(this.URL))
{
X.Add(m.Value);
}
for (int i = 0; i < X.Count; i++)
{
rt = rt + X[i];
rt = rt + "_";
}
return rt;
}
}
}

To use the code, copy this code into your project, and declare the class, like

//replace http://yourURlhere.com with your own url in the bellow statement
FileNameFromURL ff = new FileNameFromURL("http://yourURlhere.com");
string File_Name = ff.CONVERT();
//use the File_Name to save your documents, etc..,