The application was perhaps written in c/c++ as well--compilers are open source.
If your application is internet-aware or -capable, then it relies heavily on open source software.
Do you use putty for any connections? FOSS.
SSH? FOSS.
My point is that you can't get away from it. It's all around, and you rely on it quite a bit more than you may know.
It is all C# with some T-SQL. The MS C++ we have left is quickly being gutted. I said I will not embed any open source into our app. I am firmly aware of how TCP/Ip and other protocols work I have been doing this for over 25 years and started before the internet craze.
The only browsers we support are IE and Firefox (yes I know) but they are entered externally. We do not use any of that code internally.
No putty.
Yes and most of the problems we do have is the crap we have to talk to.
/johnny