The emulation of old console games on PC is a complicated subject, and one we've written about extensively, as in this piece on The ethics of emulation: how creators, the community, and the law view console emulators. Nintendo's approach is a more straightforward one. They don't like it.
Two ROM-hosting websites, LoveROMs and LoveRETRO, are the target of a recent lawsuit by Nintendo (a pdf of which is hosted at TorrentFreak). There's a lot in that 27-page filing, but here's an explanation of why these sites in particular have been chosen, out of all the similar sites that exist.
"The LoveROMs website alone receives 17 million visitors each month. Such visitors are drawn to the website by the widespread availability of free, unauthorized copies of Nintendo’s video games and other highly valuable intellectual property. The resulting popularity of Defendants’ LoveROMs and LoveRETRO websites has allowed Defendants to reap substantial ill-gotten gains, including through donations and the sale of advertising on the LoveROMs and LoveRETRO websites."
In response LoveROMS has removed all Nintendo games, although games for other consoles remain available there, while LoveRETRO "has effectively been shut down until further notice." However, the lawsuit calls for a lot more than that. Nintendo are after statutory damages of $US150,000 for each Nintendo game hosted on the sites and up to $US2,000,000 for each trademark infringement, as well as a handover of the domain names and the sources of their ROMs.
At this point it's fun to bring up the fact that the version of Super Mario Bros. for sale on Nintendo's Virtual Console was found to be a ROM that someone at Nintendo had downloaded off the internet. If you're not up on that story, here's Chris Bratt (formerly of Eurogamer, currently running People Make Games) to tell it.