From GameBrew - a wiki dedicated to Video Game Homebrew.
DSecure is a Flashcard security Homebrew. It is able to lock flashcard, protect high scores and savegames with a password, changeable by a text file.
DSecure is open source, and it is released under GNU General Public License v3.
It was part of the NEO Summer Coding Compo 2009, ranked 7th under APP section.
When you start DSecure (DSECURE.nds), it replaces flashcard loader with itself.
When you reboot DS, DSecure asks you the password. If password is correct, it'll restore original flashcard loader.
When you play, all is normal, but when finished, open DSecure and DS will be protected.
R4 Revolution For DS
EZ Flash V/Vi/V+
Acekard 2 (not 2i)
Top Toy DS