Quote: &lt;i&gt;"Well, let’s imagine I own a software house and I make this applications with this incredible algorithm. I spent one year paying for developers to study and come up with my product. I would want to make it profitable, so I have to sell it as a closed-source product. If someone needs this special feature, or improvement, I would be happily to sell a special version to them. That’s the way of making enough money to cover for the investment. If I had released it in opensource, I could have saved 75% of the time with external help from other programmers, but I wouldn’t make enough money, because some other company that had better implementation in the market would sell the service of setting up my application, and custom modifications. I wouldn’t like that."&lt;/i&gt;

Like GSP said above, if your magic algorithm is to be used by half a dozen people, no one cares if it's open-source or not. If it's used by more people, you don't need to close source it. Just use the proper tools at the right time: patents!

Patent the algorithm (if it's really something magic and new), launch the code as open source (the patent will describe the algorithm anyway), and make a clear statement that you licence the patent for free for non-comercial use. This way the community wins something (they will complain anyway, but that's life), and you win as you won't have any competition for a while.