Mocking up old console games on the PC is a complicated topic that we've written extensively about, as in this article on emulation ethics: how creators, the community, and the law see console emulators. Nintendo's approach is simpler. They do not like it.
Two ROM hosting sites, LoveROMS and LoveRETRO, are the target of a lawsuit recently by Nintendo (a pdf file of which is hosted at TorrentFreak). There is a lot in this 27-page submission, but here is an explanation why these pages were chosen by all similar sites.
"The website of LoveROMs alone receives 1
In response, LoveROMS has removed all Nintendo games, although games for other consoles remain available there, while LoveRETRO was "effectively shut down until further notice". However, the lawsuit demands much more than that. Nintendo are seeking a statutory $ 150,000 compensation for every Nintendo game hosted on the sites, and up to US $ 2 million for each trademark infringement, as well as a handover of domain names and the Sources of Their ROMs
At this point, it's fun to bring out the fact that the version of Super Mario Bros. available on the Nintendo virtual console is a ROM that someone on the Nintendo Internet downloaded. If you do not talk about this story, it's Chris Bratt (formerly of Eurogamer, who runs People Make Games) to tell it.