If you have a Google Alert or Talkwalker to alert you whenever your name shows up on the Internet, you've probably recieved more than one notice about your book being available someplace it shouldn't be. Most of these evil groups use a promise of your book to phish for credit cards. Some really have pirated versions of your book... either way, it's not a bad idea to OFFICIALLY copyright your book!
You can register a work with the United States Copyright Office-Library of Congress here.
It's $65 per title, which can add up fast if you've written a lot of books, but you can always knock them off one a month or every other month until you catch up. :)
