Porn sites and viruses go hand in hand these days, it seems. That, and they often cost money - you wouldn't want to support the porn industry financially, right? Better for your kid to go to a torrent site, like torrentspy or whatever, check their archives, read the comments - porn (and other stuff) with viruses get spotted by the community quickly, and it's free porn. No viruses, no money, no problem!
...well, unless of course some porn studio sues you for downloading their stuff without paying for it. My point is... stay away from porn sites if you don't want to infect your computer. You're fairly likely to end up with your behind stuffed full of adware, anyway... or one of those annoying redirecters that sets your startup page to www.meatspin.com or whatever. (Not safe for work. Contains loud music and... meat.)