It was a legal iTunes purchase that helped the feds nab Artem Vaulin, the alleged proprietor of KickassTorrents (KAT), the world’s biggest purveyor of illegal torrent files. The irony is almost too much to bear pointing out. But according to one lawyer familiar with the ins and outs of copyright infringement, the case could have sweeping repercussions on how torrents are regulated.

First a refresher, if all this talk of torrents sounds so 2006 to you: BitTorrenting is a way to share large files over peer-to-peer networks, and it's frequently used for pirating movies and television shows and music. But it's been in steady decline in recent years, thanks in part to the rise of viable paid streaming options like Netflix and Amazon Video. A recent report from Sandvine pegs BitTorrent as comprising less than five percent of total daily traffic in North America. It’s still large enough, though, to have made KAT a very big business, according to the criminal complaint [PDF] that the Department of Justice filed yesterday.

In that report, the feds allege that KAT is the 69th most-visited site on the Internet, with over 50 million unique visitors each month. That volume means that not only does KAT allegedly cost copyright holders millions, by enabling downloads of first-run movies for free, but also that it’s able to take in nearly $17 million in annual advertising revenue. That kind of popularity, combined with a tendency to dismiss valid copyright takedown requests, combined to make KAT an obvious target for law enforcement.

“Websites such as the one seized today brazenly facilitate all kinds of illegal commerce,” said Richard Weber, chief of the IRS’s Criminal Investigation unit, in a prepared statement. “[We are] committed to thoroughly investigating financial crimes, regardless of the medium.”

Authorities arrested Vaulin, who is Ukrainian, in Poland, where he now awaits extradition. The Department of Justice seized seven domains affiliated with KAT, all of which are currently down. Law enforcement used a warrant to obtain an email and IP address associated with Vaulin that showed up in multiple iTunes purchases, and was used to log into the official KAT Facebook account. That, combined with a Whois and GoDaddy search, a financial trail, and messages that identified Vaulin’s known alias as “KAT’s purported ‘Owner,’" left investigators with little doubt as to his role in the site.

If convicted, he faces a maximum sentences of five years in prison for each count of criminal copyright infringement and conspiracy to commit criminal copyright infringement, along with 20 years for conspiracy to commit money laundering. But that's a very big if, says Ira Rothken, a technology-focused lawyer who most notably defended Kim Dotcom during MegaUpload’s legal troubles. Authorities shuttered that site in 2012. There are superficial similarities between the two situations—copyright infringement, a lucrative advertising business—but MegaUpload was functionally very different from KAT. The former allowed users to upload any file (including a pirated movie) and create a unique link to share it, while KAT used BitTorrnet's peer-to-peer sharing technology. In other words, MegaUpload housed the files itself; importantly, KAT did not.

“We’re not aware of any case in the history of the United States where hyperlinking, or the use of torrent files, was ever found to be direct [copyright] infringement,” says Rothken. “In my view, without direct infringement you can’t have a criminal infringement.” Instead, Rothken says, torrent-related copyright cases have historically fallen under the purview of civil courts.

“There are no content files on KickassTorrents,” says Rothken. “They’re just linking information.” He points to a case like MGM Studios vs Grokster, in which the Supreme Court held that peer-to-peer file-sharing companies could be sued for any infringement that happens under their auspices.

“One infringes contributorily by intentionally inducing or encouraging direct infringement, and infringes vicariously by profiting from direct infringement while declining to exercise the right to stop or limit it,” wrote since-retired Justice David Souter in a unanimous opinion. That latter phrase certainly seems to apply to KAT, which Rothken says is all the more reason it should be a civil, not criminal case. In fact, Rothken says, it's possible that authorities are using KAT as a test case, to exert greater control over how torrents are regulated.

“There’s no doubt that this has the tell-tale signs of a test criminal case,” says Rothken. “If the defense prevails, then the Department of Justice can point to this scenario to tell Congress there may be a need to update the criminal copyright laws.” And if KAT loses, there’s now legal precedent to bring criminal charges against torrent operators. (The most famous precursor to the KAT case, the Pirate Bay, was tried in Sweden, and was a joint criminal and civil procedure).

As for the domains, those listed by the Department of Justice all appear to be down, but a cursory Google search turns up least one active site appears to house an unofficial mirror of KAT. It's just one of several sites claiming to house a copy of KAT, many of which may simply be password traps, as TorrentFreak notes.

Individual users of KAT while it existed likely don’t have much to fear in terms of criminal liability. It’s very hard to prove direct infringement in the context of a torrent site, Rothken says. Still, proceed with caution.

“To the extent that anyone is acting in a way that’s risky, it would be likely that the site’s being highly monitored by a governmental authority,” says Rothken.

In other words, now’s not a great time to use KAT—or to be the guy who allegedly ran it. And if the case ends with a conviction, it’s going to be a bad time for torrents all around.