Access to e-mail and other Internet resources is very much a necessity for conducting business and accessing information. However, along with the convenience that network connectivity brings, this also raises serious security concerns. With always-on connections such as cable modems and DSL lines, Internet users need to be increasingly vigilant of security issues, as network traffic coming into the computer can modify, damage, or steal files and programs even when the user is away from the computer and the computer is idle. In conjunction with other security measures, tools such as firewalls can help to prevent such damage.

Firewalls are used to enhance security of computers connected to a network, such as a LAN or the Internet. A firewall separates a computer from the Internet, inspecting packets of data as they arrive at either side of the firewall - inbound to, or outbound from, your computer - to determine whether it should be allowed to pass or be blocked. Firewalls act as guards at the computer's entry points (which are called 'ports') where the computer exchanges data with other devices on the network. They ensure that packets that are requesting permission to enter the computer meet certain rules that are established by the user of the computer.

Firewalls operate in two ways, by either denying or accepting all messages based on a list of designated acceptable or unacceptable sources, or by allowing or denying all messages based on a list of designated acceptable or unacceptable destination ports. Although they sound complex, firewalls are relatively easy to install, setup and operate.