Shields Up! is a free online Internet Vulnerability Profiling tool on the http://www.grc.com/ website.
This tool, I've known for quite sometime and is one of the most useful, if not a usefule website that scans your PC/Home network/Network for various internet vulnerability including known commonly used Ports scan, All well Known ports scan, Messenger scan, Browser header scan.
It scans and reports the results in a nice graphical format that any novice can easily understand and take precautions.
Click here for Shields Up!