When anyone or anything can access your computer at any time,your computer is more susceptible to being attacked.You can restrict outside access to your computer and the information on it with a firewall.

What do firewalls do?
 

Firewalls provide protection against outside attackers by shielding your computer or network from malicious or unnecessary Internet traffic.Firewalls can be configured to block data from certain locations while allowing the relevant and necessary data through
They are especially important for users who rely on "always on" connections such as cable or DSL modems.

What type of firewall is best?
 

Firewalls are offered in two forms:hardware (external) and software (internal).While both have their advantages and disadvantages,the decision to use a firewall is far more important than deciding which type you use.
 

• Hardware
  

Typically called network firewalls,these external devices are positioned between your computer or network and your cable or DSL modem.Many vendors and some Internet Service Providers (ISPs) offer devices called "routers" that also include firewall features. Hardware-based firewalls are particularly useful for protecting multiple computers but also offer a high degree of protection for a single computer.If you only have one computer behind the firewall,or if you are certain that all of the other computers on the network are up to date on patches are free from viruses, worms, or other malicious code, you may not need the extra protection of a software firewall.Hardware-based firewalls have the advantage of being separate devices running their own operating systems,so they provide an additional line of defense against attacks.
 

• Software
  

Most popular operating systems (Windows XP, Windows Vista, Mac OS X) include a built-in firewall;if yours does,consider enabling it to add another layer of protection even if you have an external firewall.If you don't have a built-in firewall,you can obtain a third-party software firewall for a low cost or no cost from your local computer store,software vendors,or ISP.Turn off any built-in firewalls before installing a third-party software firewall,and never have two software firewalls running at the same time.Although relying on a software firewall alone does provide some protection,realize that having the firewall on the same computer as the information you're trying to protect may hinder the firewall's ability to catch malicious traffic before it enters your system.