Not only is this a violation of copyright, it's no different than pick-pocketing--it's stealing. Like my author friends, this has happened to me, and each time I feel violated, angry, frustrated, and helpless.
I hate sounding like a commercial for an accident attorney, but if you're an author and this happened to you, there are steps to take.
1. Use Google Alerts. By setting up a few keywords (your name, book titles), you're alerted every time there's a new web result through Google.
2. Write a letter. Send a "cease and desist" email to the site adminstrator. This (I've found effective) and other tips can be found in the article "How to Combat Book Piracy".
Don't let this dampen your creative passion. Take a deep breath, re-group, and write on!