Given the explosion in subscription and ad-supported music streaming services, I thought the old war between the music industry and sites specializing in music piracy was pretty much over. Maybe you did too.

Not so fast.

It seems that the war has not ended so much as morphed. In the early and mid-2000s, music piracy rested on a couple of pillars: playing or ripping music from an illegally copied CD, and disseminating music through peer-to-peer file sharing sites.

If you want to rip music from a CD today, you first have to get your hands on a physical CD without paying for it and then find an optical drive to rip it with – not an insurmountable task, sure, but probably more trouble than it’s worth for most people. LimeWire and Napster (at least in its original incarnation) are long gone, and while file-sharing sites still exist, the ubiquity of ad-supported and subscription streaming services means that it’s often easier to access music legally than it is to pirate it, a major shift compared to Napster’s heyday.

But one vestige of the iPod era hangs on, and has even recently expanded, in the form of sites that let users convert YouTube videos into downloadable music files without paying the dollar or so that iTunes or Amazon would charge for the track. The practice is called “stream ripping.”

Before we go on, a warning: The popular site youTube-Mp3.org shut down last year, but many similar sites are still out there. I wouldn’t touch any of them, and if you value your device’s security, I don’t think you should either.

YouTube-Mp3.org shuttered last fall after a coalition of record labels represented by the Recording Industry Association of America sued the site. The parties settled, and while the terms are not public, the final judgment was entered in favor of the labels on all counts. It is not hard to see why YouTube-Mp3.org settled rather than continuing to fight. Such sites do not pay to license the music they allow users to download. Labels and publishers get paid when their intellectual property appears on YouTube. While individual streams are not typically worth much, when someone downloads the audio (or the video) and plays it back on their own device again and again, the lost royalties can add up.

Several other stream ripping sites recently went dark under public and private pressure from the music industry. Unfortunately for the music industry, there are so many of these sites that it seems unlikely they will all vanish anytime soon. Unlike peer-to-peer sites, where an active user base is essential, all a stream ripping site needs is the requisite technology. And, as the Electronic Frontier Foundation has observed, the sites aren’t illegal by definition. Creators who aren’t record labels may make their work free to use or share under an arrangement such as a Creative Commons license. Like torrenting, it isn’t the activity itself that is illegal; it’s the fact that so many people use stream ripping to violate copyright.

At least, stream ripping isn’t illegal in the United States. A Danish court recently ruled that a stream ripping site, Convert2MP3, operates in violation of the law, and ordered internet service providers to block it.

Stream ripping isn’t new, but some reports suggest its use has increased, especially among teens and young adults. “As soon as we think we’ve come up with an innovative solution [to piracy], the pirates seem to come up with an even more innovative infringement tactic,” Pippa Hall, chief economist at the U.K.’s Intellectual Property Office, told the BBC.

After years of decline, the music industry is doing nicely now. The RIAA’s year-end report for 2017 showed revenue from all recorded music grew 16.5 percent compared to the year prior, and nearly two-thirds of that revenue came from streaming. The industry still hasn’t bounced back to the highs of the late 1990s, but it has enjoyed several years of robust growth all the same. New business models have evolved, and copyright laws are in the process of catching up.

But just like piracy on the high seas, the problem of pirated intellectual property waxes and wanes without ever fully going away. The music industry, along with other owners of valuable IP, has to adjust its responses to an evolving black market in its wares.