Apparently there is a new trojan/virus out there that is leaving Windows XP SP 2 systems extremely vulnerable to a trojan/virus. Apparently if you visit a site with the appropriate image in IE you will become instantly infected. If you download the image in firefox you will also become infected.
Right now there is no fix to prevent you from getting infected. I would hope something is coming to us fairly soon.
You can read more information about this threat: http://www.theinquirer.net/?article=28590
Seems like this could turn into a major problem before all is said and done.