This puzzle is part of the Monthly Topic Challenge #1: Restricted Title: xkcd 1xxx

I’ve been tasked with auditing a certain computer. I was advised that the owner of the computer might have deleted some evidence before handing it over. Upon inspecting the file system, I found to my relief that no files had been recently deleted, and all their contents and time stamps were intact. But I noticed something very odd: all of the file extensions had been removed. Here is the file listing of the disk:

audio/homophonescompressed.___              02:17:05
audio/homophonesrawrecording.___            03:13:00
emus/wine/system32/recyclebin.___           15:04:10
emus/wine/system32/spinninghourglass.___    19:16:07
puzzling/prooffermatslast.___               09:21:20
puzzling/theultimatechessstrategy.___       12:00:06
scripts/bash/wordmatcher.__                 22:01:00
scripts/python/anagramer.__                 11:14:00
scripts/typescript/rot13.__                 18:08:00

Who am I and what has the owner of this computer been up to?


1 Answer 1


Who am I and what has the owner of this computer been up to?

You are working for a fiscal authority and are trying to find evidence of tax evasion.

The file extensions ...

... can be derived from the nature of the files. They are:

    .oga: an OGG Audio file
    .wav: an uncompressed sound file
    .ico: an icon
    .ani: an animated cursor
    .tex: a TeX source file for typesetting formulas
    .pgn: the portable game notation for chess games
    .sh: a shell script
    .py: a Python script
    .ts: a typescript source file

The timestamps ...

... have the curious property that each number from 1 to 22 appears only once, either as hour, minute or second. They probably represent a kind of order. There's also a correspondence between the three letters of the file extension to the three numbers (hh:mm:ss) in the timestamp. (For the files with two-letter extensions, the seconds are zero.)

The letters from the extensions and the hh:mm:ss numbers can be seen as sequences. The first letters are O, G, A, W, A, V, …; the first numbers are 02, 17, 05, 03, 13, 00, …

Now create 22 empty slots. Put the first letter O into slot 02; put the G in slot 17 and so on. (If the number is 00, do nothing.) A message is spelled out:


The answer to which is


  • $\begingroup$ @M Oehm, Very nice, everything in your answer is exactly right. However it is missing a final step that @JLee has almost identified: what is the answer to the question you have discovered? hint: rot13(gjb jbeqf) $\endgroup$
    – caPNCApn
    Commented Jul 14, 2022 at 12:22
  • $\begingroup$ Oh, I see. Let me extend the answer ... $\endgroup$
    – M Oehm
    Commented Jul 14, 2022 at 12:39
  • $\begingroup$ @MOehm, nice job. You've solved it. Sorry I made the final answer so convoluted. Mind if I make a slight edit? $\endgroup$
    – caPNCApn
    Commented Jul 14, 2022 at 12:57
  • 1
    $\begingroup$ Note that in the US at least, you must still pay your taxes on time. Filing an extension only grants you additional time to file the paperwork. $\endgroup$ Commented Jul 14, 2022 at 19:37
  • 1
    $\begingroup$ @pacoverflow To learn the very limited nature of the U.S. federal income tax, and start paying only what you owe (which is zero for most of us), see here, here, and here for more. You're welcome. $\endgroup$
    – JLee
    Commented Jul 16, 2022 at 13:42

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