After an exensive legal battle, Nintendo has finally managed to get the R4DS flash cartridge banned in Japan, making life more difficult for Nintendo DS pirates, and legitimate homebrewers
The R4DS flash cartridge is a nasty thorn in Nintendo's side, but they've won an important battle against it in Japan. The cartridge allows users to pirate Nintendo DS games, simply by dragging a downloaded game onto an SD card and then plugging that card into the slot on their cartridge. Then, they simply pop it into their DS and they are good to go.
Nintendo has been fighting a legal battle against the R4DS cart for years, and it's been illegal to sell in Japan for quite a while. In fact, this spring, a retailer in Saitama, Japan was arrested for selling the cartridges. It was the first time an arrest was made for this, but unfortunately, it hasn't warded off retailers from continuing to sell the cartridge.
The R4DS cartridge and accompanying microSD card.
A major issue is that up until now, it has still been legal to import the R4DS into Japan, something which Nintendo finally put an end to. The Japanese Ministry of Economy, Trade and Industry has announced that as of now, it is prohibited by law to bring the flash cartridges into the country.
Unfortunately, as with most battles against piracy, there is some collateral damage here. There are plenty of people who make perfectly legal homebrew applications for the DS, but which won't be accessible anymore as you need an R4DS cartridge to use them. In addition, there are people who simply back up their DS games on an R4DS, keeping every game in one place instead of having to travel with dozens of game cartridges. These people are out of luck too.