Well, if you really want to know, try
Nessus
http://www.nessus.org/ (if you have access to a linux system on the network)
Ethereal (a sniffer program, Windows or Linux)
http://www.ethereal.com/
Retina (you can download a demo) (Windows)
http://www.eeye.com/html/Products/Retina/
Ethereal (a sniffer program, Windows or Linux)
http://www.ethereal.com/
Snort (Intrusion Detection, incase someone is trying to hack your system, Linux or Windows)
www.snort.org
Retina is the only one that costs money, and Nessuss is close to it and free, but Nessuss only runs on Unix / Linux type stuff.
Use these to scan your computer. Retina nad Nessuss will give you a guide of what it found and if it is a security hole, how to fix it.