Yeah we all know that the 3DS was hacked on launch (well sort of) but no Nintendo is claiming that if you use a flash cart or try running pirated content through other means the company could send a firmware update your way and brick the system. This is similar to the security measures taken by Sony and Microsoft where they would ban users from their respective networks (PSN and Xbox Live) who play pirated content or become a nuisance but Nintendo is going out for a full on brick. When Nintendo was approached regarding this issue they replied:

“We do not discuss product security details (for obvious reasons), nor can we discuss the details of countermeasures available in the Nintendo 3DS system. Nintendo 3DS has the most up-to-date technology. The security has been designed to protect both the creative works in the software and to protect the Nintendo 3DS hardware system itself.

So we would recommend you guys to not buy any used 3DS’ for the time being until this matter is situated.

Source: GoNintendo