what are firewalls for?

Giganews Newsgroups
Subject: what are firewalls for?
Date: 28 Dec 2006

I was listenening to Kim Commando on the radio, and she said that if
you have a computer without a firewall, a antivirus program, and an
antispyware program and you go online for a few minutes, your computer
will be filled with spyware and viruses.
How does this happen?  How can these files be dumped on your computer
over the internet?

Also: One thing I notice is that I frequently get a message in a little
white window at the bottom of my screen, saying that "files have been
upgraded, click here to install".  Just what am I installing anyway?
Is it safe to listen to these messages?

Also, I had a computer without a firewall hooked up to my internet
service, and then I replaced it with another computer that had a
firewall.  Since the old computer had ports that could be found on the
internet, does that mean that the new replacement computer can be found
by the hackers?
Security Newbie