Closed source

In computing, a program is closed source when the source code is not available to any user, that is, it is not made public. It is called as opposed to open source.

Programs such as Microsoft's Skype, Adobe's Reader, and Microsoft's Windows operating system are examples of closed-source proprietary software. Since the source code is not available, there is no way to analyze what the program does or does not do, which is why problems related to privacy and security often arise for the systems in which they are used.

Proprietary software generally uses closed source. Due to its quality as an industrial secret, its disclosure and modification could constitute a crime in some countries such as the United States and several in Europe, and those who engage in this practice are prosecuted.