You don't have to buy a firewall program, as there are many free ones available
such as Zone Alarm or Sygate. Zone Alarm is great for novices or those users
that do not know [or want to know] much about tcp/ip. They are available at the
link below.
http://www.snapfiles.com/Freeware/security/fwfirewall.html
Firewalls block access to ports from untrusted networks such as the internet. To
actually close a port you need to disable the associated service or application
which may not be practical if the port is used for networking on a lan for
instance. A utility such as TCPView will show what process/executable is using a
port on a computer. Installing certain applications will open ports on your
computer which a properly configured firewall will protect from unauthorized
access. I also recommend a NAT router, preferably one that also has an SPI
firewall, if using a cable/DSL modem. Software firewalls can become
misconfigured if not careful or even disabled by a malicious program or software
conflict.. --- Steve