In Nintendo’s constant vigilance to protect their consoles from homebrew programs and other backdoor entry, Nintendo has currently pulled Citizens of Earth from the eShop. Citizens of Earth (which was just included in the recent Nintendo Humble Bundle) contains an exploit in the boot-up screen that can allow 3DS owners to run unsigned code on the console — assuming you already have an existing point of entry like Cubic Ninja or broswerhax.
Citizens of Earth — a love-letter to the iconic Mother series — launched late January 2015 from developer Eden Industries. There has been no official statement from Nintendo regarding the removal, though it isn’t unprecedented. Another indie title VVVVVV was similarly removed from the eShop earlier in May for having the same sort of exploit.