Nintendo released a statement on their website yesterday, regarding the 3DS Swapnote application, known as Nintendo Letter Box in other regions. According to Nintendo, they have recently learned that some users may be exchanging their friend codes through online message boards, making them susceptible to inappropriate messages from strangers. Due to this, the family friendly company has decided to end Swapnote's SpotPass feature, preventing users from sending and receiving messages over the internet. Special messages from Nintendo will also cease as of now. The official statement conveys that they are doing so primarily to protect underage users.
We are very sorry for any inconvenience to the many consumers who have been using this service responsibly; however this decision was made considering the point that many minors also use this feature of Swapnote. Thank you for your understanding.
Nintendo's message ends by urging parents to check out the company's parental control settings. It is unsure as to whether pending messages that were sent before the cut off will still make it to their destination, though it seems unlikely. While this may feel like a step back for Nintendo, the company has stated before that they plan on bringing the Wii U's Miiverse service to their handheld at some point in the future, which could easily replace Swapnote and all of its functionality.