F-Secure is a security software company that has been making good products for a long time. They have published a new tool that scans your computer for vulnerabilities and provides a report on what programs you need to update.
The application runs inside Internet Explorer and requires Window XP or Vista. Try it out here, http://support.f-secure.com/enu/home/onlineservices/fshc.shtml
Note that this doesn’t replace anti-virus software. It only checks which programs on your computer are vulnerable to attacks and need to be updated.