File > Properties > StatisticsTAB will show who last SAVED the
file........and when it was last accessed...............don't know how to
tell who last just opened it without saving..........

Vaya con Dios,
Chuck, CABGx3

If you are referring to files in the 2007 file format (*not* 2003 and
earlier format), you can look at the XML files that make up the Excel file.
Excel 2007 files are really Zip (compressed) files which contain a number of
XML files as plain text (a concept that should have security and audit folks
quite alarmed).

Using your favorite Zip program (e.g., WinZip, PKZip, SecureZip), unzip the
XLSM or XLSX file. You'll get a number of files and folders. In the docProps
folder, open the Core.xml file in Notepad or your favorite XML Editor (I use
XML Spy from Altova). There, search for the string

<dc:creator>

This element contains the user who last used the file.

Maybe this is what you saw

http://j-walk.com/ss/excel/odd/odd26.htm

Regards.