Lorelle has an excellent post covering spinning spam – “Spinning Spammers Steal Our Blog Content“. As always, the article is full of useful links and insightful quote.
Here is a quote from a linked article – “Protecting Your Content From the Spinning Spammers” – describing the issue:
 […] process of modifying the content before reposting it is often called “spinningâ€. Spinning a work before republication has several advantages, the largest of which is that Google is less likely to detect the work as a duplicate and, thus rank it higher. However, almost equally important is that it is much harder for victims of plagiarism to detect and follow up on the misuse, making this kind of abuse much harder to stop […]
Here are some helpful tips for detecting the stolen content:
- Digital Fingerprinting: Digital fingerprinting is a process by which you append a unique word or phrase to the end of your posts in your RSS feed. If the feed is scraped, so is the fingerprint and searching for that string of characters tells you which sites have taken your content. Since fingerprints don’t have easy translations or synonyms, they remain intact through the spinning process. Plugins such as the Digital Fingerprint Plugin and Copyfeed can automate the process.
-  Trackback Monitoring: As was the case with Tony’s original post, spam blogs often leave links in the scraped post intact, even as they modify the copy. They often send trackbacks to those URLs in a bid to get extra incoming links to the spam blog. If you link to your own articles when writing, you can watch the trackbacks and get an idea for who is using your content, even if it is spun.
-  FeedBurner Tracking: FeedBurner offers a very powerful “uncommon uses†feature that tracks where your feed is published. Since FeedBurner does not depend upon the post content to track the feed, spinning the text will not fool the system.
I tried digital fingerprinting coupled with monitoring a few times and I have to say it works pretty good. The way I was doing it though, was on a per article base, not for the whole feed. I noticed that when my content is stolen, usually just a few articles are taken – presumably those with high ranking keywords.
So, what I do sometimes is invent a new word (wordativity anyone? blogalerting?), stick it in the post, and then setup Google Alerts for this word. The moment Google indexes something with this word, I am notified either via an RSS feed or an email. (If you feel really paranoid, you can create a new Twitter account, pipe the RSS feed to that account, and folow it with your main account, so that you get an SMS when stealing occurs.)
Anyway, check the above links for more information about the problem, some insight into legal point of view, as well as how to handle the cases when this happens. And spread the word too.