What Do you Do With Your Published Work Which Might Be Stolen?

Frankly, I'm talking about money; the ammount that I stand potentially to lose. I have to admit that I was a little bit annoyed to find a "copy" of my work on Amazon.com. I was terribly unimpressed that there is another book on the site that looks very much like mine.

How did I find this out? I used sales rank express, and lo and behold, on Amazon there is another book entry for In Search