Is an open source prototype a bad idea?

I'm building a prototype for a web/mobile application. The goal is to collect user generated content, let user rate it while at the same time being entertained and do something interesting with it. If I can collect a fair amount of data, there are interisting business opportunities.

Instead of keeping the prototype closed, I use github for source control (and backup). I don't mind that the source code is now open source (EDIT: and publicly available), because nobody really understands the idea behind the application yet. I don't think there is a great risk.

Am I wrong?

EDIT:
I do know the difference between public and open source, and I do know how to check the pricing plans on GitHub. This question is not about price or about where to find a place to stash code, it's about what really are the risks of publicly developing something that will be used for a business.

Open source has its purposes. It also has its purposes in a fully commercial environment.

Take Video platform company Kaltura.com for instance. Their codebase is open source, people improve on their video players, contribute code back to the company base, create a community of developers and a buzz that keeps Kaltura's solutions known to more and more people. The company makes a living selling the content delivery (e.g. hosting). In that case there's a clear advantage to being open source. Everybody wins.

"Using github for backup, and I don't mind people taking the source code" as you put it is not a valid business reason to go open source. If you benefit nothing from people who will gain access to the source, don't make it available to the public.

gitHub charges about $7 a month to store up to 5 private repositories. Until you find a really good reason to have your solution open source, my advice to you is to keep it private.

There is a distinction that you may need to draw here.

Open Source means a certain kind of licence (see http://opensource.org/ ) - it's not a synonym for public. Whether that kind of licence is an appropriate one for your business and your code is something that you'll have to decide.

I'm unsure whether github requires projects on their free plan to have opensource licences - but that may well be worth checking.

If you're worried about this at all it seems to be a foolish economy. A private repo is not an exorbitant amount on github. There are many cheap/free options for backups.