how to disable menu before login in asp.net ?

<div class="clear hideSkiplink">
               <asp:Menu ID="NavigationMenu" runat="server" CssClass="menu" EnableViewState="false" IncludeStyleBlock="false" Orientation="Horizontal">
                   <Items>
                       <asp:MenuItem NavigateUrl="~/home.aspx" Text="Home"/>
                       <asp:MenuItem NavigateUrl="~/profileform.aspx" Text="Profile"/>
                       <asp:MenuItem NavigateUrl="~/signupform.aspx" Text="Sign Up"/>
                       <asp:MenuItem NavigateUrl="~/changepasswordform.aspx" Text="Change Password"/>
                       <asp:MenuItem NavigateUrl="~/Holidays.aspx" Text="List of Holidays"/>
                       <asp:MenuItem NavigateUrl="Leaves.aspx" Text="Attendance"/>
                       <asp:MenuItem NavigateUrl="~/SalarySlip.aspx" Text="Salary Slip"/>
                       <asp:MenuItem NavigateUrl="~/signinform.aspx" Text="Loan Detail"/>
                   </Items>
               </asp:Menu>
               </div>