A firewall is a type of software that monitors all incoming network traffic while you're online and allows in only the connections that are known and trusted. Without a firewall, your computer is basically an "open door" to hackers. All of your private information such as passwords, credit card numbers you've used for online purchases and documents that you don't want to share with anyone are all available for hackers to steal. Whether you have a dial-up, broadband or DSL connection, every minute that your computer is connected to the Internet, it is at risk