Without a firewall, your computer is operating under an "open door" policy. Bank account information. Passwords. Credit card numbers. Documents and photos that you don't want to share with the world. They are all available to anyone with bad intentions and basic computer skills. Hackers can get in, take what they want, and even leave open a "back door" so they can turn your computer into a "zombie" and use it to attack other computers.Every minute that your computer is connected to the Internet, either through a dial-up (modem) connection or through a broadband (DSL or cable) service, it is at risk.