Like a lot of people here on HN, I'm very much against software patents. I have a pretty good idea (or so I think), but don't want to go and patent it. I want others to use my idea without restrictions.
My main question is, how can I stop someone from stealing my idea, requesting a patent and then force others to pay a license fee to use this idea?!?
Also, for the cost of an EU+US patent you can probably make a very good start on the actual product, beating your ripoffers by time instead of court.
To avoid someone else patenting it, prove that you had the idea before their patent was filed. I've heard of people doing this by writing it down in a letter and mailing it to themselves. The postal stamp works as a date.
Better, however, is to ditch stealth mode altogether, start blogging from the start. This may get you copycats, but probably also customers.
Simply publishing it on your blog describing how it works will stop it being patented as it will be the Prior Art. If you develop any code for you demo you can than choose to license that code under an open source license, BSD if you don't mind people selling something built with your code and GPL if you want anything people make with your code to remain free.
It is worth reading up about all the different licenses to get an idea of which one most closely matches your ideals.
This, but keep in mind that if you reveal how it works or it's obvious how it's working you'll open yourself up to patent trolls, who will almost always have an earlier patent similar or broad enough to sell to a jury. Sometimes it's best to keep the idea a trade secret.