A computer hacker is any skilled computer expert that uses their technical knowledge to overcome a problem.
These Hackers create custom exploits and discover zero day vulnerabilities before they can be patched to exploit systems steathily.
A pro computer hacker develops their own tools and takes on longer and more challenging engagements than a Hacker.
These hackers are strong enough to pass their knowledge on to others and thus are known as Gurus of their specific knowledge base.
Ninja specialize in stealth and ninja hackers are no different, they use stealth to hide their actions and work in the shadows.
These are the hackers that know everything about computer systems and can exploit any system with ease.