The mechanism this attack uses is interesting. So way back in the early "web 2.0" days, "trackbacks" were a big deal. You'd mention someone else's blog post on

The mechanism this attack uses is interesting. So way back in the early "web 2.0" days, "trackbacks" were a big deal. You'd mention someone else's blog post on your blog, your blogging software did an XML-RPC call out to their blog, and a notification showed up in their comments that there was further discussion on your site. It was great, and contributed to the whole community feeling of "web 2.0". But it was easily exploited by spammers, who just sent out XML-RPC calls to build links. "Pingbacks" are like trackbacks, except the referenced blog requests the URL that supposedly links back to it to verify there's actually a link there, and it appears that's what's being used to redirect the DDoS to the target server. The obvious solution is to disable pingbacks. But they exist for a reason, and even if most people don't use them anymore there's going to be an uproar from the people who still do. Keep in mind there are still people pissed that blogrolls (links) were removed from WordPress core a couple versions ago. When was the last time you even heard the word "blogroll"?