An idea I've been working on was recently posted to Hacker News and described in the same exact way.
It's an imitation, but for people who think sharing is going to make your idea better beware. It's a pretty obvious attempt to copy what I was doing and if they didn't describe it in the exact same way I wouldn't have thought much of it. Obviously, I talk too much.
Before you ask, no my project isn't finished. They're faster/better coders than I am. Yes, I'm an idiot for talking about it out loud in the first place.
Protesting and giving details would just give it more attention, so I'm content with this message. Shut up about your ideas and just work on them ---> giving this advice to myself.
If there is a decent market for your product / service, then there is likely room for multiple competitors. At that point, it's all about implementation rather than speed to market (though speed to market is still important for you because the faster you get the product built the faster you are able to start seeing money from your efforts.)
History backs this up with examples everywhere. Don't worry about people stealing your ideas.