Firewall

A firewall is like a security guard that monitors and controls the traffic coming into and out of your computer. Firewalls can help protect your computer against many threats, including malware and intruders.

Information is sent across the Internet in the form of chunks of data called packets. A firewall works by examining each packet and deciding whether or not it should be sent along to your computer. It uses a couple of different methods to decide if a packet is okay or not. One is to make sure that the packet comes from an acceptable domain name and IP (Internet Protocol) address. Another is to close certain “ports” (i.e., pathways through which others can connect to your computer).

Firewalls can be either hardware or software. There are many software firewalls available, including Norton's Personal Firewall . Your computer may even have a firewall already installed on it. The Windows operating systems such as Windows XP and Windows Vista  include a software firewall that is turned on automatically. This built-in firewall is described in more detail here . Also, some routers come with hardware firewalls built in.