Written by Michael Zhang and Sean Anderson, Writeup by MegaAbsol
What kind of file is this (format_deception.nds)?
After you manage to open the .nds file, (if you don't know how, Google is your best friend), look around for your flag. Maybe go against your first instinct.
$ file format_deception.nds
format_deception.nds: OpenDocument Text
$ libreoffice format_deception.nds
A document with the flag inside.
d0nt_judg3_a_file_by_1ts_ext3nsi0n