Distributed.Net-Why Isn't ALL Of The Source Open?

nullset writes "I was browsing on distributed.net's site, and noticed this article that talks about why the client isn't fully open source. Most of the source however, is available. The article says that they haven't opened the entire source because of the worries of people faking packets. They even mention that this really ISN'T secure, but they're looking for a better solution. What would you do in this case?" Once again, it's the ever present case of Security Through Obscurity. The old argument aside, are there cases where it works well enough? Is Distributed.Net secure enough in their position where they can keep things closed, or would opening the rest of the code help in any way?