The source code is the property of the programmer or the company making the application. Unless they want it open source, they won't give anyone access. It is like inviting anyone to copy whatever ideas, routines, program parts he wants for their own applications. A company selling an application should never give rivals access to the source code. If anyone is not trusting the company, simply don't use the application. The damage will be far less than leaking the source code to everybody. Besides, why they don't just sandbox the application before using it? They could install it in a virtual isolated environment and test it thoroughly. And when they feel it is safe, they can install it on the real computer.