I found this free software that scans your pc and detects software vulnerabilities and code flaws, alerts for installed programs that expose you to security threats and lists the latest security updates and patches you need to install. It also gives you the link to the relevant upgrade.
I scanned my pc and it found some programs needed an update such as: old version of firefox I had installed aside to the latest version I have, ancient version of Adobe Reader, stale JRE, vulnerable Windows Media Player (6.x ...), .NET framework needed to be patched and some other flaws.
After I found some trojan horses on my machine last week, this is a tool I recommend wholeheartedly.
Secunia Personal Software Inspector (PSI), download here: