May 2000. An attachment called LOVE-LETTER-FOR-YOU.TXT.vbs lands in millions of inboxes, and Windows helpfully hides the last extension, so everyone sees a harmless text file and double clicks it. Within ten days it has been through the Pentagon and the British Parliament, and done billions in damage. The tell was always there, in the name: two extensions where there should be one.
Objective
Report where the extension that Windows showed the user actually starts.
Steps
$ hidden_extension_at("LOVE-LETTER-FOR-YOU.TXT.vbs")
19
$ hidden_extension_at("a.b.vbs")
1
$ hidden_extension_at("notes.vbs")
-1
Expected files
Allowed functions
None. Write every helper yourself.
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