Up in alt.binaries.multimedia.aviation, a guy by the name of Waldo Pepper is posting pdf copies of Squadron books, and similar type books. If your isp has a decent retention, then there are quite a few up there for you to pick up. I just found it the other day, so I don't know how many he's posted.
What, you mean as opposed to uploading the latest Hollywood blockbuster, videogame, PC application or hit album like everyone else seems to be doing these days? Not defending it, just stating the obvious.
I thought that copyright, patents, designs, and trademarks covered intellectual property.
ISBN is a worldwide standard for identifying specific books and a few other things - it's a standard for keeping track of specific publications, but it doesn't assign rights. The official ISBN standards and manuals don't say anything about intellectual property rights.
As far as I'm aware, just because something has an ISBN doesn't mean that it is a "registered intellectual property". Such intellectual property might have an ISBN but doesn't have to have it. In fact, some books have ISBNs and are not copyrighted, i.e. there's no intellectual property right retained by the author or publisher.
Squadron probably has a good case for copyright infringement against Waldo, if they can track him down, and if they can prove economic harm.