A hacker is a person skilled in information technology who uses their technical knowledge to achieve a goal or overcome an obstacle, within a computerized system by non-standard means.

Though the term hacker has become associated in popular culture with a security hacker – someone who utilizes their technical know-how of bugs or exploits to break into computer systems and access data which would otherwise be unavailable to them.

Among security hackers, there are several types, including:

1. White hats are hackers who work to keep data safe from other hackers by finding system vulnerabilities that can be mitigated.

2. Black hats or crackers are hackers with malicious intentions.

3. A grey hat is a computer hacker or computer security expert who may sometimes violate laws or typical ethical standards, but does not have the malicious intent typical of a black hat hacker.

More Info: en.wikipedia.org