Someone whose above-average grasp of a system lets them access classified information and computer environments.
A hacker is traditionally any individual who has a strong understanding of computer systems and can therefore manipulate them as they like. Such an individual’s grasp of computing networks and environments allows them to modify software without the original developer’s approval, and access areas inaccessible to ordinary computer users.
In contemporary times, the term has a negative undertone and usually refers to people with bad intentions to breach computer security systems and steal confidential information. There are, however, different categories of hackers based on intention and action. In descending order of negative motives, these are black hackers (bad), gray hackers (neutral), and white hackers (good).