Prety much anything is more secure than C, because the language doesn't offer any support for the programmer. No matter how careful one is, a simple mistake could lead to a (potentially exploitable) crash.

Modern C++ can be written in a secure way, however, this requires more discipline and knowledge when compared to languages such as Java or C#, which are very forgiving with programmer errors.

As for what software is written in, that depends. For Linux, I guess that's C and C++. For Mac it's mostly Objective-C, C and C++. For Windows probably a mix of C#, C and C++. On iOS it Objective-C and C or C++, but new apps will maybe move to Swift. On Android it's mostly Java, with some C and C++. Web apps don't use C or C++, however, they're not as hot as they used to be, mobile is the cool thing now.

As one can see, there's actually a lot of C and C++ in production or still being written.