A common perception among people is that a Hacker is a person who can find out your hotmail or yahoo password. They think Hackers are those who do all malicious things like breaking into systems and write Viruses.We should blame Hollywood for making movies like Die Hard and Italian that showed some nerd accessing Top Secret FBI files and gaining full control over Traffic system :)
In fact someone who break into system and do malicious things is known as a Cracker. These are the people who just uses software tools to break system. Tools they use are basically Sniffers, Key Loggers and Trojans. On the other hand a Hacker is a Person who make good software, share it with others and identify loop holes in the system.
Hackers are good Programmers who spend sleepless nights working on Problems and to help others. They have no intention to break into systems. Even if they break into system, they just do it for identifying loop holes.