A system can be compromised in any number of ways, the most common being "hacking". Hacker is a term often used to describe someone who tries to break into computer systems. Eric Raymond, compiler of The New Hacker's Dictionary, defines a hacker as a clever programmer. A "good hack" is a clever solution to a programming problem and "hacking" is the act of doing it. The terms "Hacker" and "Hacking" have been adopted by the media and the general population.
Steps for Recovering from a UNIX or NT System Compromise