Port 80 Information
World Wide Web HTTP
HTTP is used to serve and request WWW pages. The Source computer has scanned your computer for a Web Server. Personal Web Servers, while common, are not always secure. Some Personal Web Servers can be used to gain access to files on your computer. Many Trojan/Worm attacks spread via this port (such as the infamous Code Red). The firewall is protecting you from this threat. However, if you are running a web server or are publishing web camera photos to the web and that application is not working you will need to open this port.
This is from »www.hackerwatch.org