Have any of you e-book authors had your material copied without payment?

I have been writing with the hopes of getting my material self-published as an e-book. I had a Facebook friend post recently that a friend of hers, who had done the same, had her book copied by some people onto their device without having to pay for it (something like that). Basically the material was able to be obtained without having to pay. She expressed her worry about that happening to her since she was about to publish her own work and someone commented that she just needs to go ahead and do it and hope people pay for it. I am in the same boat as her with the worry and wonder how often this happens. Even though I know there's a chance I won't get much money from my books, there is a chance to make a living on it if it's successful, but not if people can get it for free. Does that happen a lot? Is there a way to ensure people can't get it without payment? I believe she used kindle publishing if I'm not mistaken. I've heard of people having success there and being able to make money so I'm not sure what to think and it's discouraging.
Added (1). And just to be clear, I'm not referring to people copying it and trying to sell it as their own. I'm talking about people copying it somehow, just to be able to read it for free.
Added (2). There are books in certain genres that make a killing apparently, and yes many use Kindle publishing.

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