[Namrog84]

Doesn't have to be open source. Just cause you don't have the source or its not free doesn't mean you can't still fuzz it. Though If some company is running some home brew solution then yes. But plenty of people run services based upon technologies that are semi widely available. Even if not open source.

[eridius]

True, you don't need the source, but you do need the service. And my point was that the software you can run are the software providing the underlying support for the service (e.g. HTTP handling with Nginx, databases with Mysql, etc), and is not the service directly.