how to hide gridview column in exporting gridview data to excel file

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Drawing;

/// <summary>
/// Summary description for GridviewExportUtil
/// </summary>
public class GridviewExportUtil
{
    /// <summary>
    /// 
    /// </summary>
    /// <param name="fileName"></param>
    /// <param name="gv"></param>
    public static void Export(GridView gv)
    {
        HttpContext.Current.Response.Clear();
        HttpContext.Current.Response.AddHeader("content-disposition", "attachment;filename=DataExport.xls");
        HttpContext.Current.Response.Charset = "";
        HttpContext.Current.Response.ContentType = "application/ms-excel";
        using (StringWriter sw = new StringWriter())
        {
            using (HtmlTextWriter htw = new HtmlTextWriter(sw))
            {
                //  Create a table to contain the grid
                Table table = new Table();

                //  include the gridline settings
                table.GridLines = gv.GridLines;
                //  add the header row to the table
                if (gv.HeaderRow != null)
                {
                    //string lastHeaderText = gv.HeaderRow.Cells[gv.Columns.Count - 1].Text;
                    //if (lastHeaderText == "Select")
                    //{
                    //    gv.HeaderRow.Cells[gv.Columns.Count - 1].Text = "";
                    //    gv.HeaderRow.Cells[gv.Columns.Count - 2].Text = "";
                    //    gv.HeaderRow.Cells[gv.Columns.Count - 3].Text = "";
                    //}
                    GridviewExportUtil.PrepareControlForExport(gv.HeaderRow);
                    table.Rows.Add(gv.HeaderRow);
                }
                //  add each of the data rows to the table
                foreach (GridViewRow row in gv.Rows)
                {
                    GridviewExportUtil.PrepareControlForExport(row);
                    table.Rows.Add(row);
                }
                //  add the footer row to the table
                if (gv.FooterRow != null)
                {
                    GridviewExportUtil.PrepareControlForExport(gv.FooterRow);
                    table.Rows.Add(gv.FooterRow);
                }
                //  render the table into the htmlwriter
                table.RenderControl(htw);

                //  render the htmlwriter into the response
                HttpContext.Current.Response.Write(sw.ToString());
                HttpContext.Current.Response.End();
            }
        }
    }
    /// <summary>
    /// Replace any of the contained controls with literals
    /// </summary>
    /// <param name="control"></param>
    private static void PrepareControlForExport(Control control)
    {
        for (int i = 0; i < control.Controls.Count; i++)
        {
            Control current = control.Controls[i];
            if (current is LinkButton)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as LinkButton).Text));
            }
            else if (current is ImageButton)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as ImageButton).AlternateText));
            }
            else if (current is HyperLink)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as HyperLink).Text));
            }
            else if (current is DropDownList)
            {
                control.Controls.Remove(current);
                //control.Controls.AddAt(i, new LiteralControl((current as DropDownList).SelectedItem.Text));
            }
            else if (current is HiddenField)
            {
                control.Controls.Remove(current);
            }
            else if (current is CheckBox)
            {
                control.Controls.Remove(current);
                // control.Controls.AddAt(i, new LiteralControl((current as CheckBox).Checked ? "True" : "False"));
            }
            if (current.HasControls())
            {
                GridviewExportUtil.PrepareControlForExport(current);
            }
        }
    }
}