A Hacker is a program designed to infiltrate a system. They are designed to easily get past security systems and create elaborate codes to secure things they wish to keep safe. Most other programs have a very poor opinion of hackers.
Hackers operate much like Code Masters. They provide a professional service to anyone for the right cost and have no real preference what the job details, providing you never betray or double-cross one. Unlike many people on the Net, Hackers will actually perform contracted work for viruses, something that gets them into huge trouble with the Guardian Collective. Because of such involvement they are generally treated as criminals.
Hackers do not naturally belong to any one system and as a result their icons are not formatted to ReBoot in a Game Cube. If they ever wind up inside a Game they will be trapped.