> Are there more Windows exploits and vulnerabilities knows and documented because of the larger user base or because it is less 'secure' than Linux/OS-X?
Yes.
You may think this to be a flip answer, but it isn't. Both factors play a part. Windows is notoriously insecure because of how it evolved (at the hands of so many people over so many years, with different priorities and skill levels), but it is the primary target of hackers (a) because it is full of gaping holes, and (b) because of its large installed base.
