martinibuster - 3:46 pm on Nov 19, 2012 (gmt 0)
The bad news
Stolen content is common. Once a site ranks the content will be stolen. It's not a matter of if the content will be stolen. It will be stolen.
I once busted somone who had scraped my part of my site and was selling it on eBay as an Instant Website for AdSense package. I once had to send a takedown notice to a university dean because a professor had stolen an entire article, used it at a conference, then posted it online with links to all my competitors. Yes, it's pretty ugly out there.
The good news
It used to be that stolen content would cause our pages to rank less well. The effect is not as dramatic anymore. Google's ability to identify the correct document is vastly improved and I find I don't have to chase infringers anymore.
You might benefit however from chasing down the highest profile infringers, like infringement on sites with decent pagerank, and especially infringement on .edu sites.
Can stolen content lead to Panda?
Whether this is Panda related, site unseen, just to hazard a guess and a shot in the dark, I'd say probably not. Stolen content is everywhere. It happens pretty much to every site that has ever ranked for a keyword. Stolen content is so widespread that if that could lead to Pandalization there would be massively widespread collateral damage.