Shortly after its release in Japan, hackers demonstrated that, yes, the 3DS could run an R4 cartridge, the notorious piracy medium that has given Nintendo fits throughout the lifespan of the DS. That was to be expected, as the R4 is a DS medium, and the 3DS is backwards-compatible. The 3DS cartridge is a different format.
Well, the veil around that has been punctured.
pirates concerned citizens who pirate back up their legitimately-purchased and owned copies of 3DS games may be interested to know that "Crown3DS", a new flashcard developed in the middle of last month, is capable of running Splinter Cell 3D. It'll take some time to get the thing down to a manageable and distributable size, but hackers have proven it's possible. Ball's in your court, Nintendo lawyers.
3DS Hacked -- First Footage Shown [Button Combo]