When you first open your excel application use these settings
excel.IgnoreRemoteRequests = true;
excel.Visible = false;
As an aside instead of using
icrosoft.Office.Interop.Excel
throughout your code e.g.
Microsoft.Office.Interop.Excel.Application excel = new Microsoft.Office.Interop.Excel.Application();
try putting
using xl = Microsoft.Office.Interop.Excel;
and then you can use
xl.Application excel = new xl.Application();
which makes things a little clearer