Index.of.finances.xls.39 -

If I rename to .xls or .xlsx , Excel just crashes. Hex dump shows 39 00 00 00 at offset 0x1A, which might be a version marker.

I was going through some legacy financial archives from the late 90s/early 2000s, and I came across a strange entry in a folder list: Index.of.finances.xls.39

Index.of.finances.xls.39

Does anyone know what the .39 suffix means? If I rename to

DataHoarder_99

Found Index.of.finances.xls.39 in old backup—what is this format? Index.of.finances.xls.39

It was listed inside an Apache Index of /finances directory listing (raw). The actual file extension is not .xls but .xls.39 .