We understand that this is a very sensitive issue, and that every author has their own position on it. We also know how hurtful it feels to find your book has been pirated; Peter Armstrong, a Leanpub co-founder, published two books with a traditional publisher, and both were pirated.
With that said, our opinion is that authors should just ignore piracy.
Our belief is that piracy is a smaller problem than obscurity. The best thing to do as an author is to just take the effort that you would have spent sending copyright takedown notices to pirates, and spend that effort instead on writing blog posts excerpting and promoting your book. Chances are this will be a more profitable use of your time.
Our intention is not to trivialize this important issue. When people see their hard work being ripped off it initially makes almost everyone very upset.
If you do want to fight any particular instance of piracy you have discovered, you can issue a copyright takedown notice to whomever it is you believe has infringed on your copyright.
How you do this may depend on your jurisdiction, or the jurisdiction of the alleged infringer. To learn more, the best thing is to do a web search for "copyright takedown notice", or even look for the website's own takedown policy; here's ours: https://leanpub.com/takedown.
(If you're interested in our policy on DRM, please see this article.)