One objection to open source software is that it allows everyone to see what goes on in a program - and some of those people might be dishonest. That being the case, some people suggest that software be kept a secret, that the source code not be published. They think that in this way, it will put up an obstacle to help discourage malicious crackers from exploiting weaknesses in the software. Keeping aspects of a program secret is sometimes referred to as "Security Through Obscurity."
The following quotation about lock smithing explains why security through obscurity isn't effective.
