How Can I Block Website From All The Browser Using C#.Net?

private void btnBlock_Click(object sender, EventArgs e)
{
            String path = @"C:\Windows\System32\drivers\etc\hosts";
            StreamWriter sw = new StreamWriter(path, true);
            String sitetoblock = "\n 127.0.0.0 www.facebook.com";
            sw.Write(sitetoblock);
            sw.Close();
            MessageBox.Show("Site Blocked");
}