Can someone steal my writing if it's not copyrighted?

Your work is copyrighted from the moment you write it. Ideas, however, cannot be stolen.

Amateurs waste time on this crap for no good reason. A very high majority of amateurs don't have anything worth stealing in the first place so you are worrying for nothing.

Yes. Anybody can take your ideas; they cannot be copyrighted, and I bet you anything that even your ideas have come from another author's work. I'm not accusing you of anything by the way - every writer out there would have used basic ideas from another story, a movie or TV show. So if you try to copyright ideas you're fighting a losing battle.

But the content you write is protected the moment you write it. Characters etc. are covered, so people who steal them are setting themselves up for being sued. Or if people copy your entire plot with no effort to change it. To be honest though no amount of copyright will stop people who are determined - just looking at the number of pirated movies and best-sellers out there should be clue enough that everything is vulnerable. So you can either accept that someone out there might attempt to steal your book and post it anyway, or live in fear that someone will steal it and keep it to yourself.

Everything you write is automatically protected by copyright the minute you write it. You don't have to do anything else.

If you post your work ("copyrighted" or not), or even publish it in a printed book, then yeah, somebody might "steal" it.

However, nobody is going to steal it, and your concerns about that are childish and amateurish. Anyway, "ideas" can't be copyrighted at all. Only the actual words expressing the idea can be copyrighted.

If you wrote it, it is copyrighted. However, read the terms of service (TOS) carefully. You may give up certain rights if you post something to the site. You certainly give the site the right to post your work.

Added:

1) If you have written something of commercial value, you should reconsider posting it on any site because publishers will consider this "previous publication," and that will affect what they might be willing to pay to use it or may affect their willingness to consider it all.

2) There is no copyright in general ideas. Someone would have to copy many unique details of your story to be in copyright trouble. Not to worry, however. Anyone who could make a marketable story of your idea, already has half a dozen better ideas before breakfast.

Even a copyright is not an absolute guarantee that someone will not use your work, but if they do you can sue them.

The only thing copyrighted is the exact wording. The concept is not, but plagiarism is when someone steals your work word for word, or in what is obvious paraphrasing of your work. This protection is based on who can prove that they produced the wording first.

There are some scam artists out there who will try to convince someone that they had the wording first in order to try to get money for "damages". If you have a copy of your works in a dated source (even as simple as an email to yourself, or the dating of your upload to a web site,) you have the proof required to prevent anyone from claiming the work as their own.

I can steal your words and copyright them via the government copyright office, but if you walk into court with any document proving that you produced it before me, I will lose the case and face formal criminal plagiarism charges!

That's not what copyright law does.

Yes if it's not copy righted someone can steal it copyright it and claim it.

I think I've heard of that happening before.

I mean... I would be afraid of the same thing.

Yes! OF coursE! Just copyright it, and none can steal it!