The article doesn’t say how the domain was “taken over.” Since they haven’t reverted the website back to its original content, it sounds like either the author or the publisher (whoever owned the domain) did not renew the domain and the domain is showing content from its new owner. Its terrible that a link in a kids book now leads to a porn site, but the lesson is to not let domain registration lapse.
A less insidious version of this happened to me recently when I discovered that a link in my resume that used to go to an article featuring an interview I gave (on a journal website owned by a large and respectable institution, though not on their main domain) now goes to some teenager’s video game diary. Apparently the publication collapsed, the institution gave up the domain, and I was none the wiser. Harmless but embarrassing. I changed all the links in my resume to archive.org links.
Books are solid things that will be here for a long time. Websites are transitory, ethereal and likely to change. It's clearly ok to reference a book from a website, but books that reference websites - yeuch. It reminds me of those stacks of hard-copy programming manuals targeting specific versions of a language now obsolete.
When you don't understand this you end up in this kind of situation. If you don't renew your domain, you might lose it (as the author and publisher are now finding out). I expect legal proceedings will fail miserably, and that a nice fat bung will probably solve the problem immediately.
Depending on how much penetration (no pun intended) your work has, it can be used as an amazing distribution channel.
