Online piracy has ravaged the music business and now it’s about to do the same to the games industry, thanks to a device the size of a thumbnail. Once known only to hackers, the R4 Revolution is currently the fifth biggest-selling electronics item on Amazon’s UK web store - priced at £12.57 including a 2GB memory card.

It is marketed as a legitimate device that enables gamers to store copies of Nintendo games they have already bought for their portable DS console, negating the need to carry cumbersome cartridges around. However, as some gamers have discovered, the device also stores games downloaded direct from the internet. This means that rather than paying £20 for a game, they can download it free from filesharing sites.

In the past these illegally downloaded games wouldn’t play back on a DS console because of inbuilt copy protection software. The R4 circumvents this, leading to a freeloader frenzy as gamers rush to buy the device then load it up with free games.

The scale of the problem has forced Nintendo to act. Last month it launched a lawsuit in Japan against importers and marketers of “game-copying devices such as the R4 Revolution”. Nintendo also said it is working closely with authorities in 11 countries - including the UK.

The problem is that the device itself is not illegal. “It’s the purposes that people use it for that’s often illegal,” says Rob Saunders, a spokesman for Nintendo UK. “When you fill a memory card with hundreds of downloaded games - that’s theft.”

Exactly how Nintendo intends to wage its war on piracy in the UK is unclear. Will it follow the music industry’s lead and press internet service providers to freeze the accounts of file sharers – or even mount private prosecutions, as the British record industry has done? Nintendo says it has asked Amazon to stop selling the device, but last week there was no sign of this, with R4s still selling well. If the music industry experience is anything to go by, the signs for Nintendo - and other gaming companies - are ominous.