Internet Privacy - This is Downright Scary

Think that anything you do can remain a private matter in this age of the Internet? Think again.
I was well aware that just about everything is available online if you know where to look. I knew, too, that hackers occasionally break into even the most secure systems. I was naive enough, however, to believe that a story I was writing and in no way whatsoever was connected to the Internet was my own to do with as I wished. This is a story only halfway complete and I am not even sure how it will proceed because I haven't got that figured out yet. I haven't even given it a name, just have it stored as a WORD document listed "secret assignment."
Imagine my surprise when, while looking for something else, I found it on the Internet along with my street address and email address. I know that someone with a little knowledge of computers will say , "Don't worry, it's only available on your own computer."
Oh, sure. Until a hacker decides to seek out my hard drive or until I accidentally do something that makes it available to the world. If it's on there at all it can happen.
Not only that, but anyone who manages to call it up can change the story however they wish to, can take the plot and twist it a little for their own use, can type in their own ending and submit it to a publisher. I know because I experimented a little and found it was possible to work on the Internet version just as I would by calling up the original document.
This does not make me happy. It does not make me feel secure. It makes me wonder just how much a copyright is worth today. Theoretically anything you write is copyrighted from the moment you type the words even though you may later do it formally. But if someone can read your work the instant you hit a key to update it...well, I'm not so sure it really works that way any longer.
I have other stories that are in finished form stored under "My Documents." Are they also available to anyone with the knowledge and ability to find them? Probably.
I don't come even close to being a computer expert. To me a computer is much like a car, something to use when you want to do something. I've driven cars for more than sixty years but haven't a clue as to how they work. It's the same with computers. They are great for writing stories or looking up things on the Internet, but what makes them operate is a mystery to me and I prefer to keep it that way.
So this problem that has come up, what can I do about it? Not a damn thing.