The Microsoft Excel file types (xls, xla, xlc, xlm, xlt, xlw) are mainly associated with Excel, Microsoft Corporation, Spreadsheet, Excel.Sheet.5, Excel.Sheet.8, soffice6.xls, Free Microsoft Viewer, OpenOffice.org, Zoho Viewer (Web Viewer), and with the following MIME types: application/vnd.ms-excel [official], application/msexcel, application/x-msexcel, application/x-ms-excel, application/vnd.ms-excel, application/x-excel, application/x-dos_ms_excel, application/xls

This SonicWALL signature identifies HTTP downloads of Content-Type: application/xls.