The internet is a black hole for artists. It's a copyright Bermuda Triangle.
This is such a convoluted topic, I'm almost too wary (and weary) to tackle it. Don't take any of my opinions as legal advice. If you, as a creative person, fear someone "stealing" your work, then take advantage of all your legal avenues to prevent it.
Here's my take: Once I put something out there, it's out there. I hope no one uses my work for profit without my consent, but there's no way in hell I'm gonna know every infraction. I do know some. I have a Google Alert set up for my book title. More times this year than I care to remember (probably six?), an alert has popped into my email box informing me that my book is downloadable for free on a site that doesn't have permission to distribute it for free.
It used to irk me. Now, I figure, maybe a few people will read it and like it enough that they'll actually buy something else I've written (or will write).
My house sits on a large lot. At one corner, three neighbors, whom I've yet to meet, place their trash on the very edge of my property for pickup each week. At first, this irked me, just like the free downloads. Now I see that it doesn't really harm me much. I've even thought about building an aesthetically pleasing trash bin for them to use. It's just a matter of being neighborly, in a way.
Are those free download sites making a killing off my download? Selling ads as an aggregator? I doubt it, but I don't know. Frankly, it doesn't harm me much. Or at least, if it does, I don't feel it directly. I worry sometimes when I find things on the internet that I want to
use but can't find a way to properly credit the creator. It's not easy
to know who created what online.
But my creative work is my work. I put hours and worry into it. I'm not going to give it away outright. Far from it. I'd like to make more money from it, but doing so isn't easy. My advice: Do what you can and when you can to keep your work protected. Then, let it go. It's going to be out there whether you double-down on surveillance or not.
For an overview of copyright issues for writers, see this post by Writer's Digest.