The Tokyo District Court has granted an injunction against the sale of R4DS carts, which enable gamers to download and use pirated Nintendo DS games.
Japanese retailers had been selling R4 carts as 'back-up devices', as have major online retailers in the UK, such as Amazon.co.uk
Nintendo's new DSi releases in the UK on April 5, which features much improved anti-piracy measures.
DSi still to be hacked
Though it is not yet clear whether or not hackers have managed to develop R4DS type carts for the DSi, it is rumoured to only be a matter of time.
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Nintendo, Square Enix and Capcom all backed the Japanese court's decision, claiming that the R4 was a "violation" of Japanese law.
Despite the Japanese ban, it looks like R4DS carts are still easy to find on sale in the UK. TechRadar has contacted Nintendo UK about this story, so stay tuned for further updates shortly.