Hacker n. : One who, or that which, hacks. Specifically: A cutting instrument for making notches; esp., one used for notching pine trees in collecting turpentine; a hack.

Example:
How is it possible for a Hacker or virus to write emails using your address?

Taxonomy
free encyclopedia, character, TV series, see List, principal character, technology, computer security, programmer, subculture, computer hobbyist, computer hackers, search, free dictionary, definitions, academia, 1960s, involvement, home computer.

Defination from the web:
Hacker (programmer subculture), a programmer subculture originating in the US academia in the 1960s, now primarily notable for its involvement in ... Hacker (hobbyist), an enthusiastic home computer hobbyist ...