Windows computers can be attacked in many ways
— and not just with viruses, worms, or Trojan horses. Another popular way to
attack a Windows computer is to attempt to communicate to it over any of the
network “ports” found on Windows computers. These ports are kind of like
TV channels or radio frequencies. Computers are set up to listen for messages
that may arrive from other computers — this is how they communicate with one
another.
How firewalls work
Firewalls monitor all the communication
between your computer and the Internet. Firewalls know what kinds of
communication are allowed to flow in and out. They know this because they have
something called an “access control list” — a list of rules that specify
precisely what kinds of communications are allowed and what kinds
