Well, I am not only a novelist but I write articles focusing on writing tips, promotion and the industry as a whole for sites. My articles pop up everywhere but a couple of times I saw my article without my name on a site with other articles without names, LOL! But I'd recognized my article because I have Google alert and whenever my articles pop up on someone's site or my name or books are being searched, I know. One of my articles popped up on one site, without my name on some site with other articles where none had names with them. But, I've never SEEN my article being taken credit for by someone else...yet. I say yet because it may have happened but I just don't know. Now, I have had my photos stolen MILLIONS of times, LOL. It peed me off at first, but then I started taking it as a compliment. You can't stop things like that.
That's the downside to the net. It's a great place for writers to reach people but unfortunately, you can't control who is reached. You can't prevent people stealing from you because if someone wants to take something then they will. The only thing you can hope for is to find out after it's done then take action.
P.S. If you have a name of the person from the site, CONTACT the person! Sometimes work is put on sites where you can't find any mode of contact. I'd definitely do that if I haven't already. It's different when you got contact info or a name. Simply write them and tell them your concerns and to take the post down. See how it goes from there. Most folks will cooperate once they've been caught. You have some who might try to ignore you, but most times they get afraid of what action you might take so they usually oblige. Threaten them with a lawsuit or something. I see writers doing this on blogs all the time, LOL.
I just put up the BY Creative Commons attribution license today. It requests attribution. I have not been actively looking for content that has been taken. http://creativecommons.org/licenses/by/3.0/us/ I am more interested in getting recognition than other things.