The TPB clone I currently use doesn't have such a warning and I don't experience high CPU usage so probably they don't mine XMR on users computers anymore. But still I have a question about the the situation we had in the past(and probably may encounter in the future). If I use such a site for 20-30 seconds to find a magnet link, and then I copy the link and close the site, does it mean that actually XMR is mined on my computer only for 20-30 seconds? I mean if what a TPB forum moderator once said was true,
then what could they gain from most users, who, most likely, were using the site the way I was?
The key to their earnings (through browser mining) lies in fact that most users still have a different habits then you. They stay a lot longer on the page looking for what interests them, so your 20-30 seconds of search for someone else can be 2-3 minutes or 20-30 minutes.
If you know what you want than it can be short visit, but from my personal experience I can tell that I need on average at least 5 minutes to pick what to download, even if know what I want. It is because I check other users comments, trying to find best file by size and number of seeds.
When all this is taken into account, there is still quite solid earnings for the remaining torrent pages which use mining scripts.