There is not a lot of recourse against the site itself, especially if the site is out of the country. If the web hosting site is U.S.A., you can send a DMCA take down letter to the web hosting site. They are under pressure to break the links of sites performing copyright infringement. You are also required to share some personal information in the letter which you should do with the hosting company NOT the offending site.
How do you find the site hosting company?
You can search domain registration on whois.com at: http://www.whois.com/whois/
Once you find the web hosting site look for their contact info or legal contact. This is usually an email address link.
Gene Quinn has a sample letter you can personalize (copy and paste into email) and send to the hosting company:
You will need the offending site’s URL for your work. Once you get that GTFO. Don’t attempt to download your book.
Advise all readers you know to avoid these pirating sites as they are known to send viruses, plant adware, spyware and do phishing scams for more personal information.
Often, if you use site buttons to make contact with the site itself, your IP will be blocked. It is best not to engage the site, but go directly to the web hosting site.
This information comes courtesy of: Law Office of Cynthia Conlin, P.A.
1643 Hillcrest Street
Orlando, FL 32803
One thing you can do to help protect yourself is set up a Google alert with your book title(s) and author name.
Yes, it is true, retail platforms should tighten up their security, but this is pretty much all we can do in the meanwhile.