If you are really concerned about keeping it "yours", then write it down and register the copyright for it in your country. I believe that sending it as a fax to someone is a proper and legal way of making it "published". If you really think that it's also valuable, file a patent application (this is not automatic like the copyright, but works on a first come, first served basis, so better be first than sorry).
The "writing it down" (and optionally faxing it) makes sure that you are the author of that specific "version" of the idea, which could come in handy later, but it's also probably the first step required to be able to distribute it "as yours" to other people and have it peer-reviewed (in a sense) by your colleagues/friends/whatever.
You could use this second "step" before applying for a patent to avoid extra costs for having to revise it should something be wrong and the initial application is rejected by the Patent Office - although the nice country of the USA allows patents on software and I'll bite my nails for the first flawless piece of software, so I wouldn't worry about flawed ideas that you might want to patent if they're worthy...
In summary, share it (publish), fix it (peer-review), and use it (?)