We had similar issues at work this week. Our DoS protection didn't kick in since it's all coming from different IPs. We ended up increasing the number of max connections and decreasing timeout values on our web servers so that each connection would not last as long. We had a few hours where we were seeing a ton of connections, but after that it's been slower (but still coming in.) Someone in our security team did some research and found others reporting similar issues, it looks like there are a few ISPs overseas who have some misconfigurations and are directing this BitTorrent traffic to incorrect IPs.
Good luck
Edit: We do business in China, so it wasn't feasible to block a broad section of Chinese IPs, I'm not sure if that would be an option for you. Found some more on it here: http://serverfault.com/questions/658433/mysterious-misdirected-traffic-how-can-i-find-out-what-dns-server-an-http-requ