How to avoid cross script reflected security issue for hidden HTML controls with in a gridview in ASP.NET with C#?

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ASP.NET

IIS

C#3.5

I want to avoid cross script reflected security issue for hidden html controls with in a gridview in asp.net with c#. I am using Visual Studio 2008 with c#.

I am fetching the hidden field values with in the gridview and in the source it is as below:

<cc1:XDataGrid ID="grdDetails" runat="server" HorizontalAlign="Center" Width="100%"
                                        AutoGenerateColumns="False" CssClass="NeST_DATAGRID_FIXED_SIZE" OnItemCommand="grdDetails_ItemCommand"
                                        AllowCustomPaging="True" AllowPaging="True" OnPageIndexChanged="grdDetails_PageIndexChanged"
                                        OnPagerClicked="grdDetails_PagerClicked" PageSize="10">
                                        <AlternatingItemStyle BorderWidth="0px" CssClass="NeST_DATAGRID_CELLDATA2" Wrap="True">
                                        </AlternatingItemStyle>
                                        <ItemStyle BorderWidth="0px" CssClass="NeST_DATAGRID_CELLDATA" HorizontalAlign="Left"
                                            Wrap="True"></ItemStyle>
                                        <HeaderStyle CssClass="NeST_DATAGRID_HEADING" Height="20px"></HeaderStyle>
                                        <Columns>
                                            <asp:TemplateColumn HeaderText="Sl No.">
                                                <ItemTemplate>
                                                    <asp:Label ID="O_SecondaryCode" runat="server" Text='<%# DataBinder.Eval(Container, "DataItem.SlNo") %>'>
                                                    </asp:Label>
                                                    <input type="hidden" id="hidID" runat="server" value='<%# DataBinder.Eval(Container, "DataItem.MandateReference") %>' />
                                                    <input type="hidden" id="hidMandate" runat="server" value='<%# DataBinder.Eval(Container, "DataItem.MandateReference") %>' />
                                                </ItemTemplate>
                                                <HeaderStyle Width="4%"></HeaderStyle>
                                            </asp:TemplateColumn>

What I have tried:

In the item command I am fetching in the same as below:

 HtmlInputHidden hidID = (HtmlInputHidden)e.Item.FindControl("hidID");
string Id=hidID.toString();