hacker

1. A person who breaks into, or attempts to break into, or use, a computer network or system without authorization , often at random, for personal amusement or gratification, and not necessarily with malicious intent.
2. [An] unauthorized user who attempts to or gains access to an information system (IS). [INFOSEC-99]
3. A technically sophisticated computer expert who intentionally gains unauthorized access to targeted protected resources. [After ANSDIT]
4. Loosely, a computer enthusiast. [ANSDIT]
5. A person who uses a computer resource in a manner for which it is not intended or which is in conflict with the terms of an acceptable-use policy, but (unlike the work of a cracker) is not necessarily malicious in intent.