I just discovered this true story on the Kindle boards and, seeing as we have a lot of self published authors here, figured you'd be interested in this. Short summary: If someone disagrees with your content and wants your book off the market, they can file a DMCA notice and Amazon (or other online bookstores) will take the book off their listings until both parties (author and complainer) agree to put it back up. Of course, if the reason is just malicious intent, that might never happen. Or the complainer could try to extort money in exchange for said 'agreement'.
I wonder if serials on Wordpress could be targeted the same way. This is really, really scary.
Make sure you've done all your copyright paperwork - though in this case, even the official document wasn't enough.