Duplicate content? Send a polite "please don't do this request." If they ignore it after 7 days, or respond with the middle finger, find their hosting provider, send a DMCA take down to their hosting provider, send DMCA requests to Google, Bing, DuckDuckGo and Yahoo! (the big four), then use the various webmaster tools to submit the offending URLs to the search engines for delisting. I would also suggest you get the list of other hosts running on the same IP as the infringing website and ensure they aren't leeching content on mirror websites.
Want to actively protect your content so they aren't removing just your links through a search & replace or automated means? Two ways to do it: 1. Rather than link directly to your website, use bit.ly or other URL shortening system that has the link instead. 2. Have alternative domains registered that 301 to your main domain, and instead of linking to your main domain in the article, use these alternative domains that will instead redirect. I probably shouldn't mention that this is also good Google Fu.
And if you want to be really blackhat, most spammers are running unsecured versions of WP with gaping security holes that are susceptible to many of the vulnerability probing tools available. Just saying...