Health Check is a free online tool designed to help consumers identify security updates needed on their computers.
http://www.f-secure.com/weblog/archives/00001356.html
http://www.f-secure.com/healthcheck/
Similar to Secunia Security Inspector, of course. The F-Secure scanner identified an out of date Wireless driver on my Windows partition which Secunia never mentioned- probably because it is not associated with any security vulnerabilities, but still good to know about.
