While Nintendo has, for the most part, successfully held off the mass proliferation of pirated software on 3DS and Wii U, it was a major issue for the DS, in particular. R4 cards, regardless of their potentially innocent use, were largely sold and utilised to download and play ROMS of DS games for free, and for a time they were easily available on the market. Nintendo's firmware and security options from day one were certainly weaker in the last generation, and piracy is still cited as one of the great problems faced in that period.
Of course, legal cases and law changes are still filtering through on this issue, with the matter only moving on in any meaningful sense in Japan last year. There are still retailers and manufacturers of R4 cards out there, too, and it seems Nintendo Spain is the latest to secure a victory in shutting down this area of business. A store in the region called ChipSpain had been selling and distributing these goods, and before the matter went to trial the retailer has now admitted fault, recognising that the import and sale of the cards was illegal under Spanish law. For his part the deputy general manager of Nintendo Spain, Rafael Martínez Moya-Angeler, has said the following (translated):
The marketing of devices that violate the protective measures of consoles and video games has led to the proliferation of illegal game downloads online. This situation has caused irreparable economic harm. Piracy is the biggest threat to creativity in this industry, so this statement is a big step forward for the gaming industry.
While the damage has arguably already been done by R4 cards, it's certainly the case that Nintendo has successfully resisted the threat — on a mainstream level — in the current generation. By pursuing older cases, it's also a show of vigilance against potential future products on 3DS.
Please pay special attention to the Community Rules when discussing this topic.