Free, Illegal Downloading

Does anyone have any ideas about what we can do about these sites that offer free downloading for books we've written? I just googled one of my titles and found two sites that offered its download for free. I tried contacting both of them, but was unable to get through.

Surely there has to be something we can do to stop them. I'm not a bestselling writer, and it really bugs me to spend months on a book just to have some inconsiderate jerk steal it from me. The book is only $3.99 to begin with.

Thanks, and I'll appreciate your thoughts.

David Berardelli