Can C be used for programming security systems

It really depends on what you mean by programming a security system. Can C be used on a particular chipset, with a particular OS to control security functions? Yes. But that is only because that chipset vendor wrote a compiler for you. Programming of a security system does not have to be limited to C. C happens to be still one of the most common languages with different embedded, mobile and larger desktop OS's varying the libraries but reusing C because of its familiar syntax.