When I save an Excel file to a folder, a second 1KB file is created with the
same name and a prefix of ~$ in front of the original file name. The second
file will not open. This never happened before. Does anyone know what it
is? and why it is there? Is it harmful? or some Office or Windows thing? If I
try to delete it, it won't delete while the original file is open? If I want
to copy the file to make a backup do I need to copy the shadow file with it?

taxes.xlsx 3,354 KB same date
~$taxes.xlsx 1KB same date
System: Microsoft Excel 2007 / Vista Home Premium
Thanks, Mark