Hackers who own botnets, malware worms that infest many computers at once and allow the hackers to control them remotely, are usually in business for themselves, selling their services to the highest bidder.  Services rendered by these botnet operators most commonly include money laundering and denial of service attacks.  Other hackers are simply guns-for-hire, paid between $1,000 and $5,000 to compromise a specific computer.  Hackers are often genius-level students who are creative and enjoy puzzles or challenges.