It was listed inside an Apache Index of /finances directory listing (raw). The actual file extension is not .xls but .xls.39 .
Found Index.of.finances.xls.39 in old backup—what is this format? Index.of.finances.xls.39
Index.of.finances.xls.39
DataHoarder_99
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. It was listed inside an Apache Index of