Check if Excel file is password protected
 

The follwing code throws up a prompt for a password when the Excel file is
password protected (it is vb.net).

ExcelWorkBook = ExcelApplication.Workbooks.Open(ExcelFullName, Nothingobj,
True, Nothingobj, Nothingobj, Nothingobj, Nothingobj, Nothingobj,
Nothingobj, Nothingobj, Nothingobj, Nothingobj, Nothingobj, Nothingobj,
Nothingobj)

How do I detect in code (vb.net or c#) if an Excel workbook is password
protected when I get the prompt for password at the same time I am trying to
open it?