A hacker is someone who likes to do new things with computers.
One wrong meaning of the word hacker is "someone who tries to get into another person's computer using computer software such as Trojan horse programs, computer viruses, and worms that can hurt other people's computers". The correct name for a person doing these illegal things is cracker, but many news stories use hacker even though it is wrong.
The older meaning of the word hacker is "someone who knows a lot about computers, and likes to do new and different or hard-to-do things with them". This meaning of the word hacker is usually a compliment. Another meaning of hacker is someone who can change or program something, like how people can change or program a Furby to say something insulting or humorous.