For when you absolutely, definitely...
realise you haven't got any and need some in a hurry.

Spybot

Lavasoftusa.com

Zone Alarm

Tiny Personal Firewall

Shields Up.
Steve Gibson's superficial port scan that should alert a "default-setup" Windows
user enough to get you to install a firewall, if it doesn't scare you off the web altogether.

Hacker Whacker
More intensive scan of many more ports and a source for security info.

File and Printer Sharing : Fact/Fiction
John Navas goes into greater detail.
WWW Security FAQ
The W3.org web server security FAQ.

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