Here is a quick way to help you figure out if the other site is stealing your content and then hiding it with cloaking:
First, look the site up in Google with a “site:www.domain.com” search. Then, see if you can view the cached page. Next, view the source code of the cached page. Then search for a unique phrase from your site and see if it shows up. If you find some of your content there, then you have your answer.
There are ways to avoid having a site’s pages cached in the search engines, and some black hatters are using these cache-busting techniques to avoid getting caught. If you (the victim) can’t view the cached page, then it isn’t quite as easy to tell if your content has been stolen. There are ways around this, but it involves IP spoofing (which is illegal). Stealing copyrighted material is illegal too, however, and some would argue that it is justifiable to fight fire with fire….. :shhh: