unknown file format please help.

I just downloaded a file it has the format TheFilename.zipo

First looking at it, I thought, ok the original file was really a zip
file but somehow it got wrongly renamed zipo.  So I proceeded to try
opening it with WinRAR.  To my biggest disappointment Winrar can't open
it and reported:  "The archive is either in unknown format or damaged."

I wasted hours trying to download it so it a real disappointment.

I wonder if anyone would know of a tool(s) I can possibly use to
determine exactly what format this file is in?  Thanks in advance.